Great new book for people who like rocks, minerals and fossils

Veteran rock hunter, writer and geologist Garret Romaine's newest book is hot off the press. The Modern Rockhounding and Prospecting Handbook (Falcon Guides; $21.95) is a great reference to keep beside your armchair and in the RV (heck, get two copies!). The book provides the knowledge you need to go from a person who likes to pick up pretty rocks (or, are they stones? See Dr. Rock's previous post) to being an informed rock/mineral/fossil hunter. Garret's book uses down-to-earth language to give you a basic overview of the geologic processes relevant to collectors; a list of common minerals, crystals, rocks, fossils, and where to start looking for them; how to collect them safely and legally; how to work in the field and the essential tools you need, such as hammers, picks, and hand lenses; and he explains what to do with your prizes when you get home from your road trip. He also tells you how to gain more knowledge: how to obtain geologic maps and how to use them, a list of blogs, and references. The book also features short interviews withcollectors and geologists (including yours truly- blush).

Garret Romaine

Garret Romaine is an avid rockhound, fossil collector, and gem hunter; he has an  undergraduate degree in Geology, a Masters in Geography, and also an MBA. He is the author of Rockhounding Idaho and Rocks, Gems, and Minerals (both FalconGuides) as well as Gem Trails of Oregon and Gem Trails of Washington. He is also a columnist for Gold Prospectors magazine. He has a raft of YouTube videos about great outings in search of cool rocks and minerals:
http://www.youtube.com/results?search_query=Garret%27s+World+Of+Geology&sm=12
 

 

What is the difference between 'rock' and 'stone'?

Doctor Rock,
Do geologists distinguish between 'rocks' and 'stones'? Are these terms interchangeable?
Louisa Mayfair
Winnipeg

Louisa,

"Hey, Callie, is this a rock or a stone?'
"Not sure, Alec, let's ask Dr. Rock!"

Nice to hear from a reader in the 'True north strong and free'.
The difference depends on the context. In the informal usage, if you apply these terms to individual pebbles or boulders, then there's no difference. You can pick up a 'rock' and toss it in the creek, or do the same with a 'stone'. However, to a geologist, that pebble is made of 'rock'.'Rock' is the accepted scientific term for the material that forms the earth's crust and deeper layers. Geologists have a simple and somewhat facetious way to distinguish between 'rock' and 'stone'. If a price tag is attached, it is a 'stone'.

Here are definitions from the Dictionary of Geological Terms ('DGT') published by the American Geological Institute:

My friend Adena is standing behind a large conglomerate
boulder. This is a 'rock' using definition 1. of  'rock'.
According to definition 2 under 'stone', this
sedimentary rock consists of many rounded stones. Click
the photo for a closer look.

'Rock' 1. an aggregate of one or more minerals, e.g. granite, shale, marble or a body of undifferentiated mineral matter, e.g. obsidian, or of a solid organic material, e.g. coal. 2. Any prominent peak, cliff or promontory, usually bare, when considered as a mass, e.g. the Rock of Gibraltar. 3., A rocky mass lying at or near the surface of a body of water, or along a jagged coastline, esp. where dangerous to shipping. 4. a slang term for a gem or diamond.
(Doctor Rock adds: "I am aghast that they left 'Led Zeppelin' out of this definition! And what about the Stones?")

'Stone' 1. A general term for rock that is used in construction, either crushed for use as aggregate or cut into shaped blocks as dimensional stone. 2. One of the larger fragments in a variable matrix of a sedimentary rock. 3. A stony meteorite. 4. A cut and polished natural gemstone; a gem or precious stone.

There are interesting variations in nongeological dictionaries. For instance, the Random House Collegiate Dictionary says, among many other things, that 'stone' is "1. the hard substance, formed from mineral and earth material, of which rocks consist." (There are 27 more definitions!) Under 'rock', that dictionary's first definition coincides with definition 2. in the DGT. The second is the 'geological definition', essentially the same as 1. in DGT.

What is the pink rock near Chinook Pass, US 410, Washington State?

Send your roadside geology question to Doctor Rock! Just add a comment at the bottom, or send an email to : tuckerd at geol dot wwu dot edu (sorry, gotta keep the spammers out!). It would be great if you could include a photo or two of the outcrop you are asking about.
This week's question:
 
Hi Dr. Rock,
When I approach Chinook Pass on US 410, heading east, on the east side of Mount Rainier National Park, the road switchbacks up a massive rock face and there is a dramatic band of orange/pink rock that cuts across the exposure. If I remember right it may be a couple hundred feet thick. Can you tell me the story of this layer?
J. McLarty

Dear J.,
You may be referring to an outcrop shown in a geology guide to Mount Rainier (the reference is below). It is located just east of Chinook Pass. Here is a photo taken from the guide book:

According to the author, Pat Pringle, well-known volcanic geologist in Washington State, the pink rock is a part of the gray rocks below. The pink portion has been baked by the slender layer of gray rock at the top of the outcrop, just visible beneath the tall trees. Hang with me here: It is a multi-stage story. The gray and pink rocks are volcaniclastic rocks, meaning they are fragmented, or broken ['clastic'] volcanic rocks. [but the term is shorter and remains 100% descriptive to folks who understand the technical lingo]. Examples of volcaniclastic deposits are ash, pyroclastic flows['hot broken'], and lahars.The term differentiates these rocks from 'solid' volcanic rocks, or lava flows. The volcanic rocks in the photo are part of the Ohanapecosh Formation, found throughout the Mount Rainier area. These rocks are 35 to 28-million years far older than the rocks of the modern cone. They were erupted from many different volcanoes that came and went over that 7 million year interval, and were buried by younger volcanic rocks and glacial and river deposits. During burial, the Ohanapecosh Formation was also intruded in many places by magma associated with these younger rocks. That is what the dark rock at the top of the outcrop is, a horizontal bed chilled magma called a 'sill' that invaded the buried rocks. The sill may have eventually connected with a vent on the surface, but any evidence for that is eroded. In any case, the hot magma baked the relatively porous rocks it intruded for  many feet above and below. Pink rocks like this are usually indicative of the oxidation caused by the baking. The photo below shows another example.

The pink band is about 3 feet thick. It is the baked zone
at the base of a massive lava flow along US 12
west of Morton, WA.

A thin band of pink rock has been baked by the
intrusion of this dike at Owyhee Reservoir in
eastern Oregon.

The guide book is:
 
Roadside Geology of Mount Rainier National Park and Vicinityby Patrick T. Pringle. It was published in 2008 by the Washington State Department of Natural Resources, and is written for  a non-technical, popular audience. There is a great Geology 101-style introduction, and mile by mile descriptions of the geology along roads all through the Mount Rainier area, extending far beyond the boundaries of the national park.
You can access the book online here:
http://www.dnr.wa.gov/ResearchScience/Topics/GeologyPublicationsLibrary/Pages/pub_ic107.aspx
The photo and description is found on page 119, part of road guide 'F'.

Volcanoes in eastern Oregon are a great geologic road trip.

Doc,
I see that volcanoes are your field of interest. I'm a self-professed volcano nut, and I'm already planning next spring's road trip, maybe to the High Lava Plains of eastern Oregon. The name alone is intriguing! I have heard there are some little cinder cones way out there. What do you know about them? Been there? Worth the visit?
Denise Hodgkins,
Port Angeles, WA

Denise,
There are indeed some young-looking cinder cones and lava flows in eastern Oregon. I think you are referring to Jordan and Diamond Craters. I've been to both areas, and they are definitely worth the visit.



Coffee Pot cone in the far distance.

The Jordan Craters are in the southeast corner of the state, off Highway 95 near the town of Jordan Valley. There a number of cinder cones and lava fresh lava flows- they look as if they erupted yesterday (read about cinder cones in my first-ever Doctor Rock post). However, radiocarbon dates indicate that the most recent eruption, at Coffee Pot Crater, was 3200 years ago. Until usable material for radiocarbon carbon dating was found, this cone was widely held to be only 1-200 years old. It is the only cone in the Jordan Craters accessible by road. Here is a map
http://www.blm.gov/or/resources/recreation/googlemap.php?lat=43.14588&lng=-117.4588
use the 'satellite' tab in the upper right to see topography. The lava flows are the dark areas. Coffee Pot erupted 30 square miles of basalt lava.
The area is administered by BLM. The round trip to the single road accessible cinder cone, Coffee Pot Crater, is 52 miles. The roads are not paved. Be wary. It's not a good idea to take a big rig in there. When I was there in the spring, snow had just melted and roads were a quagmire. I barely made it back out of there in my all-wheel-drive Forester. Pay attention to the weather, and only go after the roads have had a chance to dry out. It is remote country- no services, poor cell coverage, no help. Be smart.
There is a great route guide here: http://www.everytrail.com/guide/birch-creek-ranch-jordan-craters
The Global Volcanism Program (a must-visit site for you volcanophiles out there) has sparse information about the Jordan Craters here: http://www.volcano.si.edu/volcano.cfm?vnum=1202-19.
A pamphlet (a bit dated, from 1977) explains some of the detailed geologic features you can see in the Jordan Craters: http://www.oregongeology.com/pubs/og/OBv39n08.pdf

This is Little Red cone in the Diamond Craters.

The other place is the Diamond Craters, 40 miles southeast of Burns and Malheur Lake. The essential info is on this great website for volcanophiles: http://volcano.oregonstate.edu/diamond-craters. There are about a dozen vents in the area, and a signed nature trail takes you to many of the points of interest. The oldest cone is maybe 60,000 years old, but the youngest is a meer 6,000 or so. While you are in the area, consider traveling the Diamond Loop Back Country Byway, a 67-mile unpaved back-country drive. Well worth it!



click to open.

 

Will rising sea levels affect me?

Dear Dr. Rock,

I heard recently that with global warming, many coastal cities will one day be underwater. Is this true? Is San Diego, where I live, one of those cities? Which cities will "go under" first? Is this something that might happen in the next decade or so? Or how long?

Doug Montigale

San Diego

Doug,
I don't want to get mired in the politics of climate change. It is a topic we need to think seriously about. Sea level change due to global warming is real, though perhaps not the most critical effect (that might be weather: drought, crop failure, drinking water...). But let's attend to Doug's question.This is not, strictly speaking, a geology question, since the science of climate change is multidisciplinary. I was just looking at the new National Geographic's article titled "Rising Seas" down at the barber shop. It has a fold out map [web version here] showing sea level if ALL the world's ice melted and sea level consequently rose 216 feet*. No one is saying that climate change is going to cause that. That would be bad, but it has happened in the geologic past, when the earth was much warmer during the Eocene, first instance, and glaciers were very rare or nonexistent on Earth.
Observations show that sea level has been rising since at least 1880. Between 1901 and 2010, global sea levels rose by 19 centimeters (7.6 inches) - an average of about 1.7 millimeters (1/14 inch) per year. But looking at the last few decades, it's clear sea level rise is speeding up. Between 1993 and 2010, sea levels rose by 3.2 mm (1/8 inch) per year - nearly twice the long term average.**
Small potatoes, huh? Yeah, but that is 1 inch every 8 years, one foot in less than 100 years. Still small potatoes? That doesn't account for any increase in the newly measured 1/8 inch rate. Current projections by the National Oceanic and Atmospheric Administration (NOAA) call for sea level rise of about 6 feet globally if carbon emissions are not drastically curtailed.

The view from my deck on a sunny day in Bellingham,
WA, USA. Elevation 133 feet above the bay. Alaska
Ferry terminal in the middle ground. Click to enlarge.

What does that mean? Is San Diego going to "go under" as Doug puts it? Well, no, only those places that are less than 6 feet above sea level, and certainly not in the next decade. The Silver Strand, with the North Island Naval Air Station, is going to be submerged, or at least very precarious. In my town, Bellingham Washington, on the Salish Sea, that means that the Alaska Ferry dock will need to be repositioned, the city's waterfront parks will be submerged, the busy marina on the bay will need to replace pilings and add to the breakwater. The former site of the Georgia Pacific paper mill on the waterfront, currently being redeveloped by the city and port, will need to be designed to have a higher level grade (elevation of sea level) than at present. Bellingham is a small city. Multiply that by every coastal city in America, and you are looking at big bucks. Studies show that New York City has assets of 2+ trillion dollars at risk. Miami is worse: $3 trillion. Hurricane Sandy nearly a year ago was pretty bad. Add 6 feet to that storm surge! Then extend that to the rest of the world. Read the National Geographic article for more data and the human story. Here is a University of Arizona website with detailed maps of some coastal US cities under various sea level increases. Read a pre-Sandy New York Times article (March 13, 2012) on the expected effects of sea level rise in the near future on Americans.


University of Arizona sea level forecast map for SE USA. Click to enlarge

The principal contribution of geologists to climate change theory is showing that the geological record (that  is, rocks) demonstrate that climate change has happened in the past. Evidence for climate change is preserved in a wide range of geological settings, including marine and lake sediments, ice sheets, fossil corals, stalagmites and fossil tree rings. Nearly all the world's geological societies, which represent most professional geologists, have issued statements of concern (at the mildest) or warnings that continued carbon emissions will only increase the threat from global warming.

* That would be the pits. My home, on a hill with a nice view of Bellingham Bay, seems far above the bay at an elevation of 133 feet. Hard to imagine my lot could some day be under 83 feet of water! Even worse, those snooty neighbors a couple blocks up the street would have waterfront property! I can only hope their boat's anchor fouls on my chimney.
 **The source for my information is an analysis of the 2013 IPCC report posted on the The Carbon Brief Blog. The report is based on observations, so the data is not 'wrong'. If you don't believe in the global warming theory, fine, but you can't refute the observed data. In the immortal words of Daniel Patrick Moynihan (US Senator 1927-2003), "Everyone is entitled to his own opinion, but not his own facts." 

Are there any rock outcrops in Florida?

Dave,
I often vacation in Florida during the winter. I don't recall ever seeing a rock outcrop! Why is that? Where can I go to see rocks in Florida?
Joan Osborne
Cleveland, Ohio

Dear Joan,

The short story: there are a few areas of Florida with exposed bedrock. Virtually all of it is limestone. Your best bet is in the northeast part of the state. You won't find any bed rock in Miami, for instance. Much of the state is covered in unconsolidated clay or sand. The clays were eroded from the Appalachian highlands and deposited on top of the limestone by rivers entering the shallow sea. The sand is beach deposits. For roadside locations, see Roadside Geology of Florida by Brian, Scott and Means, and  Florida's Geological Treasures by Iris T. Comfort. I confess I haven't read any of these books, but they seem like a good place to start.

I found this map at http://www.floridacaving.com/pages/misc/karst1.htm

Dark brown areas are where limestone is at or near the surface.

This is a fossil coral from Florida. It is preserved

on a pillar in the Westlake Mall in downtown

Seattle (yep, no kiddin'! I write about it in my up-

coming book, Geology Underfoot in

Western Washington.)

The long story: It wasn't that long ago that all of Florida was below sea level, beneath the shallow warm waters of the Caribbean. Limestone is the fossilized remains of animals, many of them microscopic, that have shells made of calcium carbonate. Clams, oysters and crabs are large animals with calcium carbonate shells. When these animals die, their shells sink to the seafloor and accumulate hundreds of feet thick. With sufficient thickness, water is driven out of the spaces between the shell and they become cemented together (calcium carbonate makes great cement). If the seafloor is lifted above sea level, the limestone is exposed. The highest point in Florida is only 345 feet above sea level, so little erosion has cut into the bedrock to expose it. Your best bet to see rock in Florida is in a few road cuts, or in caves.

Florida is proud of its high

point, and has erected a

roadside sign so you don't

miss it as you drive by. It's near

Lakewood in Walton County.

The limestone in northern Florida is very young, around 50-60 million years old. It is exposed in the northern portion of the state only because the rocks have been slightly folded along a north-south axis which raised some of the rocks high enough to allow the clay and sand to largely erode away, exposing the rock beneath. The Florida Keys have some limestone, too, though it is much younger, only around 130-150,000 years old. Some was quarried to build the buildings of the Keys.

Limestone is dissolved in fresh water that is slightly acidic. The result is a swiss-cheese type of topography called 'karst'. The famous limestone caves of Florida result from this chemical weathering. Some caves must be explored by diving, but there are dry caves in the northern part of the state.

Pillow basalt

Doc,
I recently stumbled on a Youtube video showing lava flowing underwater in Hawaii. The flow was called 'pillow basalt', but I didn't understand how it formed. Is there a place to see this without scuba diving or being near lava flowing into the ocean? That looked dangerous!
Jim Gilbertson
Pocatello, Idaho

Jim
The video you saw may have been one of these:
http://www.youtube.com/watch?v=5G8W9sZtBTM or
http://www.youtube.com/watch?v=xsJn8izcKtg

They show a very small protion of a lava flow entering the ocean on the south coast of Hawai'i's  Big Island.


Pillows are blobs of lava that form underwater. The surface
hardens instantly, but glowing lava remains inside.

HOW DO PILLOWS FORM?
Pillows only form underwater, either in the sea or in lakes. Just so happens I have a whole page on my Northwest Geology Field Trips blog devoted to this very

These fabulous pillows are at Cape Disappointment State
Park at the mouth of the Columbia River.

question. I really like pillows. They are the remnants of the dynamic environment where incandescent flowing lava enters water, hissing, boiling, clouds of steam and sometimes explosions of shattered lava.

These fabulous pillows are near Orofino, ID.
Photo by Vic Camp

There are places in the US to see pillows that are now above water. You can see them near Orofino, Idaho. Another site in Idaho is on the Snake River Canyon rim a few miles downstream from Perrine Bridge
I know about sites in Washington State best, including  Hurricane Ridge in Olympic National Park, Cape Disappointment State Park, Lopez Island in the San Juans, and many places in eastern Washington (here's an example). A search of the internet found spots in California, Oregon and Maine.
If you know of some good locations, please leave directions in a comment!
Here are some places to see basalt lava pillows on dry land:
Fishing Rock State Park, near Depoe Bay, Oregon.

Avila Point, California, south of San Luis Obispo.

Rodeo Beach, north of San Francisco.

These pillows are below the lighthouse at Point Bonito, CA

Point Bonito Lighthouse, Marin Headlands, north of San Francisco.

Lake Combie Complex in the  Sierra foothills at 38°59.034´N, 121°00.366´W

Stark's Knob off  US 4 north of Schulerville, NY.

North Haven Island, Maine

 

Visiting California's San Andreas Fault

Where can I actually see/touch the San Andreas Fault? I'm visiting California in a month, and have long wanted to visit this famous earthquake fault.
Marsha Beatty
Salt Lake City

Map of the San Andreas system. USGS

Marsha,
The San Andreas fault is visible in many places. You might want to get a copy of this book to serve as your guide: Field Guide to the San Andreas Fault  (Caveat: I haven't read it, and don't know the author.)
The San Andreas is the boundary between the North America and Pacific plates. The fault extends from the Gulf of California (Sea of Cortez) northwest for 810 miles across California, from the Salton Sea trough to north of San Francisco, entering the sea south of Fort Bragg. The fault is far longer than that, as it continues into the Pacific Ocean, where it separates the Pacific Plate from the Juan de Fuca Plate.
The fault runs right through Carrizo Plain National Monument, established in 2001 to highlight the geology. The USGS has an online field guide to San Andreas features there. The National Monument is located about 160 miles north of Los Angeles, 260 miles south of San Francisco, about 55 miles west of Bakersfield, and and 50 miles north of Santa Barbara. The San Andreas is a 'right lateral fault'. That means that if you are standing on one side looking

across the fault's trace, objects on the other side have been offset to your right.

Famous sign just south of Parkfield, California.

 

The Pacific Plate is the rock on the right.
North America is the tan rock above the car.
Photo by David Lynch.

The field guide mentioned above will tell you how to find this fantastic exposure:








The patch on this road repairs damage from motion along the
fault, and has to be periodically replaced.

Try this website to visit some features in the Hollister- Pinnacles National Monument area; here and here.

This blog has photos of features along the San Andreas in the LA area.

This website is a field guide to the famous Wallace Creek site on the Carrizo Plain, probably the best-known feature on the San Andreas.




Wallace Creek--- This view of the Wallace Creek on the Carrizo Plain is perhaps the most famous feature on the San Andreas Fault. As the stream continues to progressively erode into its channel, right-lateral motion along the San Andreas Fault has moved the downstream portion of the channel northward (towards the viewer). Sediments cut by Wallace Creek were radiocarbon dated at about 3,700 years old, and the stream channel has been offset about 430 feet since then. USGS.

What causes the Basin and Range?

Dave,
I drove across US 50 in Nevada this summer. Beside being hotter than blazes, I was struck by the repeated miles-long straightaways and then steep climbs over mountain ranges. This sequence was repeated over and over. This has got to be geology, right?
Joe DeMarsh,
Dallas

Dear Joe,

You have successfully learned Doctor Rock's First Law of Everything: GEOLOGY MADE THAT! Nevada is in the Basin and Range physiographic province. This huge area is characterized by alternating tilted mountain ranges and flat valleys. These are oriented more-or-less north-south. US 50 runs right across the middle of the state, from east to west, against the grain of the Basin and Range.

Characteristic Basin and Range topography- mountains rising
several thousand feet separated by 10-20-mile-wide sediment-
filled basins. Click to enlarge any figure.

 The Basin and Range is formed by stretching of the crust in the arid US west. The crust is thin here, only 18-20 miles thick. It is spreading laterally on top of the weak, ductile mantle. This motion causes the crust to fracture along faults that are angled downward at around 60 degrees. The rock on one side of these fractures slides down relative to the other, so these fractures become faults that occasionally slip as earthquakes.The movement along these angled faults allows the crust to 'extend' laterally, east to west. There has been so much extension in the Basin and Range that the crust has stretched until it is twice as wide as it was before extension began.

Development of the Basin and Range Province
http://www.iris.edu/hq/inclass/lesson/brittle_vs_ductile_rocks

The blocks of rock that drop down along the faults form the long valleys that separate the parallel rotated mountain ranges. This topography is the signature of the Basin and Range province.



Two ways to get alternating ranges and valleys.
The Basin and Range developed via the
model on the right.



The Hanaupah fault scarp in Death Valley National Park.

The fault cuts across an alluvial fan, uplifting the mountain

range relative to the valley floor. Many thousands of small

uplifts and downdrops along faults like this are needed to

create the basins and ranges.Photo by Marli Miller
http://geomaps.wr.usgs.gov/parks/province/basinrange.html

 

Extension in the Basin and Range began around 17 million years ago and continues today. You can read about a 1983 magnitude 7 Basin and Range earthquake in Idaho here.

Basin an Range earthquakes in the first week of August, 2013
http://earthquake.usgs.gov/earthquakes/map/.

A must-read laypersons book about the geology here is "Basin and Range" by John McPhee. The book is also included in his later anthology, "Annals of the Former World". Wonderful mind expanding reading by a nongeologist.

Geology tools to keep in your vehicle

Doctor Rock,
   I really enjoy stopping along roadsides to look at rocks. I don't know much about geology but love to collect cool-looking rocks. I've been learning some things reading your blog and want to get a bit more serious about geology. What tools and books do you recommend?
Fred Armens,
Chicago

Fred,
   Good idea to have the basic tools in your vehicle- you never know when you'll want them. These would include a rock hammer (not a carpenter's hammer!) and a hand lens. You'll want eye protection when you use the hammer. A geology guide book to the areas you visit is also a good idea. A geologic map is always a good idea to have handy. If you are in an area where there are surface deposits like ash layers or lake beds, a gardening hoe is useful to scrape at exposures so you can see the layers better.

Chisel style

pick style

Rock hammers- These are made for bashing rocks. The idea is to break a hand sample off of an outcrop, or to break open a stone so you can better examine the fresh rock inside. Rock hammers come in two basic styles. Some have a chisel-shaped end, and others have a pointed pick end. The pointed end is nice for sticking into a small crack to help pry a rock loose. The chisel end is better for splitting fractures in rocks. Both work fine; it is the hammer head that you will use 90% of the time anyway. Get a rock hammer that is heavy enough to smack a rock. You might find a mason's hammer in a hardware store, but these usually  have short handles that don't give you much leverage when you swing it. There is a good description of rock hammers on this wikipedia page: http://en.wikipedia.org/wiki/Geologist%27s_hammer. Pay attention to the discussion of hammer weight. Don't forget the safety glasses! Sharp chips or dust is no fun in your eye. If someone else is swinging that hammer, keep your distance and don't watch them!
Hammers are often placed in outcrop photos to give a sense of scale. So, here's an old geology joke: How do you know a person is a geologist? They have more photos of their rock hammer than the spouse and kids!

Hand lens- By this I mean a jeweler's loupe, not the magnifying glass Sherlock Holme;s uses to read fine print and look for clues. Use your lens to look closely at a rock to see the mineral grains or fine details in the rock. Or pick a sticker out of your hand. These lenses are held right up against your eye, with the rock you are examining very near the lens. You want a 10 power (10x) lens  fro most usage. People who want more detail will find a 14x lens useful.

How to use your hand lens. First, look at the rock without the lens. See something tiny and interesting? Then mark it with your thumb, place the lens over the flashing mineral crystal or whatever you saw, and bring rock and lens to your eye. You will want plenty of light, so this method works best outside in natural light, and with the sun shining over your shoulder- turn your back to the sun.

First, spot what you want to more closely examine...

Guide books- In an earlier post I mentioned some of these. Especially useful to the layperson are the Geology Underfoot and Roadside Geology Series by Mountain Press Publishing Company. There are many other geology field guides written for a popular audience. Search the web to find something in the area you are interested in. Good idea to include 'geology field guide' in your search terms.

Then bring lens and rock up to your eye.

 

Geologic maps remind me the crazy quilts my wife makes.

Geologic map- These take some getting used to. Maybe you can find a local geologist to give you a quick lesson. There are symbols denoting faults, the orientation of rock layers, and colors for each distinct rock unit. You may find these maps for sale from your state's geology agency, or by searching the web for USGS maps.

Road map- get a good one. Your field guide may send you off on minor dirt roads that aren't shown on state-wide maps. There are topographic gazeteers to many states. Check the offerings by DeLorme.

'Small scale' vs. 'large scale' maps- The larger the scale, the more detail. I know this confuses people, it did me once upon a time. Map scales are given in fractions: 1:24,000 means 1 inch on the map = 24,000 inches on the ground, or 2,000 feet. 1:150,000 means there are 150,000 inches on the ground to one on the map ( that's 2.37 miles per inch). So, to remember which is 'small scale' and which is 'large', think of the fraction. Would you rather have 1:2 of pie, or 1:5? I don't know about you, but I'd rather have 1/2 a pie than only a fifth!

Ozark Mountain geology- an ancient sea, volcanic islands, continental collision and erosion

Dave,
   We traveled through the Ozark Mountains in Missouri and Arkansas last summer. What is the geology of this beautiful wooded hill country? What are some geologic sites to visit when we return?
Arliss Clark
Detroit

Arliss,


The Ozark region

   I visited the Ozarks when I was 7 on a family vacation. One of my earliest geologic memories is finding weapons-grade flint in the Ozarks, and watching a guy make a small arrowhead out of a piece I found.  It is wonderful country for a vacation with the kids. Campgrounds and RV parks abound. Most of what follows is from a US Geological webpage and Charles Spencer's useful books, Roadside Geology of Missouri, published by Mountain Press Publishing Company.

PLACES OF GEOLOGIC INTEREST:
Arkansas is famous for its caves, many in Ozark limestone.
A guide to Arkansas geologic sites.
Johnson's Shut-ins State Park (in the Saint Francois Mountains, Missouri): refreshing swimming holes eroded in rocks erupted on ancient volcanic islands.
Elephant Rocks State Park also in the Saint Francois Mountains, Missouri: rounded rounded boulders of 1.5-billion-year-old granite.

   The Ozarks are a part of the Ouachita-Ozark Highlands and are actually an eroded plateau. Most of the high points are of similar elevations, separated by valleys. The rocks are mainly limestone (with interbedded chert) and sandstone deposited on an ancient sea floor during the Paleozoic era (from around 540 to 250 million years ago). At the time, only volcanic islands rose above the sea anywhere around here. These islands are represented by volcanic rock, mostly rhyolite from violently explosive eruptions and the granite that cooled beneath the volcanoes. The volcanics are really ancient: 1.5 to 1.4 billion years old! Not quite as old as the 3.6 billion year old Morton Gneiss I wrote about a month or so ago, but they are the oldest rocks in the southeastern USA. The island rocks are preserved in the Saint Francois Mountains at the northeast corner of the plateau, up against the Mississippi River, but they extend a great deal further, forming the continental crust beneath the sedimentary rocks in much of the region.

Volcanic ash from explosive eruptions 1.5 billion years ago is
now rhyolite rock at Johnson's Shut-ins State Park

   Thousands of feet of sea floor sediment was deposited all around and on top of the older volcanics. The flat-lying sediment became the Paleozoic sedimentary rocks that typify the Ozarks. These rocks are seen throughout the highlands. The limestone was once coral reefs; the sandstone was eroded from the volcanic islands and deposited on the floor of the now-disappeared Rheic Ocean.

The Ozark rocks (lower center) were uplifted in a plate collision.
Click photo to enlarge and see modern state boundaries.

   But then, a gradual but huge change occurred here. During the Mississippian Period (340 million years ago) two tectonic plates were converging. What was at the time the southeast margin of North America ran up against a plate that included much of South America and western Africa. These plates were coming together to form a supercontinent called Pangea, which included all the continental landmasses until its break up around 200 million years ago. The seafloor rocks were folded and faulted as the ocean basin contracted. The collision of the plates raised a huge rugged mountain chain, much as the Himalaya-Karakoram-Hindo Kush mountains are today forming during the collision of the Indian and Asian plates. These mountains stretched across the seam (the "suture zone") marking the area of collision, which ran more or less along the equator. Remnants are the Marathon Hills of east Texas, the Ouichitas in central Arkansas, and the Appalachians. The sedimentary rocks just to the north were uplifted and tilted about a degree or two towards the south to form a plateau. These are the rocks that underlie the Ozarks.

'Dumbo' is the largest eroded boulder at Elephant Rocks State Park.
It is eroded from granite that was the source of the
volcanic rocks in the Saint Francois Mountains.

   Pangea eventually broke apart to form the modern continental and oceanic plates. The Ozark rocks have been above sea level for the past 340 million years and subjected to the attack of erosion.
   The Ozarks are famed for their limestone caves and 'shut ins'. The latter are wonderful natural swimming pools eroded in the volcanic rocks at the eastern edge of the Ozarks in Missouri.

How do we know how old a rock or fossil is?

Dear Dave,

How do geologists determine the age of an ancient volcanic eruption or a glacial advance? How do we know how many years ago Tyrannosaurus lived?
Bertina H.
Saint Louis, MO

Bertina,

Geologists, paleontologists and archaeologists often want to know the age of a soil deposit, a rock layer (such as a lava flow), or the fossils in the rocks. We speak of two types of 'ages'. 1. Relative age is the relation in time between rock layers (and the fossils they may contain). Relative age can tell us that a particular rock layer is older or younger than another. It CAN'T tell us if a rock or fossil is 3 million or 300 million years old. 2. Absolute age is the time in years before the present time. If the rock can be dated at all, the absolute age can be determined. An example: a lava flow is determined to be 32.4 million years old (almost always with some imprecision, expressed. for example, as " ± 0.2 million years").

This week I'll deal with relative age. I'll tackle absolute age in a future blog post. That will help us understand how long ago Tyrannosaurus lived.

There are some basic laws that state the principles of relative ages of rocks. Geologists apply these to the rock record to determine sequences of time.

The "Law of Superposition" says that any undisturbed sedimentary rock layer that lies above another is the younger of the two. This principal was formalized in the mid-1600s by a Dane, Nicolas Steno, who is among the founders of modern geology.

Steno's Law of Superposition says that the rocks higher in the stack are younger than those below. Sounds like common
sense now, but this was a radical thought in the 1650s, when all sedimentary rocks were held to be the same age: deposited by Noah's Flood over a period of 40 days and 40 nights.

The "Law of Cross-cutting relationships": An intrusion of magma that cuts across other rocks is younger than the rocks it intrudes. Scotsman James Hutton (1726 - 1797)



Diagram illustrating cross-cutting relations in geology. These relations can be used to give structures a relative age. Relative ages are, from oldest to youngest: A - folded rock strata offset by a thrust fault. The folding is younger than the rocks, and the fault is younger than both rock A and the folding; B - large granitic intrusion (cutting through A); C - erosional angular unconformity (cutting off A & B) on which brownish yellow rock strata were deposited; D - volcanic intrusion (a dike), cuts through A, B & C; E - even younger rock strata (overlying C & D); F - normal fault (movement down on the right side) that cuts A, B, C & E. Diagram by Woudloper.

The "Law of Inclusions": Fragments of one rock layer that are enclosed in another rock layer are older than the enclosing layer. This was also recognized by Hutton.

The Law of Inclusions: if Rock B contains fragments of Rock A, then B must be younger than the fragments of rock it contains. The intruding rock (Rock A) must have been there first to provide the fragments.    

The "Law of Faunal Succession": Englishman William Smith (1790) recognized that fossils occur in a definite, invariable sequence in the geologic record.

Law of Faunal succession: fossil remains of living things are present in rock layers at definite intervals, and exist within a discrete period of time. In this instance, using the Law of Superposition, would the age Rock Unit A be older or younger than the age of Rock Unit B?     

If you can see these relationships, you can begin to understand the sequence over time. In the case of Bertina's hypothetical volcanic eruption and glaciation, apply these methods if the deposits are in contact with each other. If they aren't both present in the same rock outcrop, it may be far more difficult to determine relative age. In a future post I'll deal with absolute dating. That involves radiocarbon and other isotopic methods. Stay tuned!
Dave

Fossilizing your RV

Here is a really off-the-wall topic. This one came in from my neighbor while we were discussing his recent camping trip. Bill asked me: "Will my camper be preserved in a rock layer some day?"



Bill's honey. Maybe a fossil someday. Like Bill.

I know that ol' Bill really loves his little Scamper trailer. His wife loves it too, because now she can send him out there when he snores. Bill wondered if there was a way to ensure his trailer would be preserved in a rock layer for future generations to admire. I explained the essential geology to him, but figured some RV.com readers might be equally attached to their rigs and have a similar idea.

Essentially, you want to create a fossil. To do it right, you have to understand how rocks are made, and what kind of rock would be needed to preserve your RV. Bury the poor thing in fine grained sediment- sand or mud. Fill the interior right up to the ceiling so it isn't crushed as rock forms over the coming few million years. Of course, I'm sure you would first obtain all the necessary permits, licenses, and variances, and you certainly wouldn't want to violate any zoning codes, right? Wouldn't want your rig dug up after only a decade when they run a new sewer line through the area! You would want to entomb your prized RV in a place that was less subject to the crushing forces of plate tectonics, or uplift and metamorphism that could squeeze and twist your pride and joy into a twisted wreck. (Bill winced when I mentioned this. Too gruesome a scene for him, so he went into his Scamper for another bottle of wine.)

"Hey Dad! I think I found something!"

 The loose sediment will form rock only if it can escape erosion. It also has to be subjected to pressure, so pick a place where more sediment can be added on top, adding pressure and squeezing the layers beneath (including your RV) into rock over the eons. Probably the best place is on the sea floor, but it wouldn't look good to just shove your camper off a boat out in the ocean. A good place might be beside a slow moving river that periodically floods and deposits new mud. You also need a spot that isn't subject to erosion for a million years or so, such as at the toe of glacier or beside a river. (Ooops! There's a contradiction. This demonstrates the capriciousness of fossil preservation, and how the same conditions that are conducive to preservation can cause them to be eroded away and lost.

Once there are a couple thousand feet of overlying sediment covering your RV, the pressure will begin to squeeze the rock grains together to make rock. That will probably be a little hard on the intended fossil, but if you filled 'er up nice and tight with mud or maybe concrete, that will be minimized.

Now, you need someone to be able to find the fossil. You can either trust to geology and hope that a new-born river will eat away at the rocks in the future and providentially expose the 'fossil', or you can cheat and post the GPS location in some place that will last forever. Maybe someone will start an Internet website to post 'intentional fossil' locations. We all know that the Internet will still make sense in a few million years, right? Plus, because there is so much wisdom on the Internet,
surely someone will know what it looked like originally.

Good luck.

The Oldest Rock in the USA

Doctor Rock,
How old are the oldest rocks in America, and where are they? How can I see them?
Jim Oldman,
Houston

Dear Jim,

An outcrop of Morton Gneiss in the Minnesota River valley

The oldest dated rocks in the USA are in southwestern Minnesota and Michigan's Upper Peninsula. These rocks are called the 'Morton Gneiss' and are 3.6 billion years old, or 80% of the age of the planet (4.54 billion). The gneiss is a metamorphic rock, meaning it began as an even older sedimentary or igneous rock, but we don't know the age of those original rocks. The oldest rocks on earth are from an Eon called the Archean. During the Archean, the cratons--the masses of rock that make up the basic, initial structure of continents--formed. The crustal bodies that formed were smaller than today's continents and are referred to as protocontinents. The oldest known anything on earth are zircon mineral grains 4.4 years old found in rocks in Australia.

Gneiss is a coarsely crystalline foliated

Archean rocks in North America

metamorphic rock resulting from extremes of heat and pressure acting on even older rocks, which deform but do not quite melt. 'Foliated' means the mineral grains are aligned due to pressure. The Morton Gneiss was formed in the intense pressure beneath a long-gone mountain range that rose during the agonizingly slow-motion collision of continental plates. These collisions brought small  land masses together to make up the interior of the North American plate.

This is classic geo-humor!

Outcrops of gneiss in Minnesota can be found near Morton, Redwood Falls, Sacred Heart and Ortonville. To get to Morton, travel west from the Twin Cities on US 212 for about 100 miles, then south on US 71 for another 15 miles to the small town. Minnesota's own EarthScienceGuy website gives more information on how to find outcrops of the rock near Morton.

But, you don't have to go to Morton to see the rock. The Morton Gneiss a widely-used building stone.

Morton Gneiss on the exterior of Seattle's
Exchange Building, 821 Second Avenue.

It is a stunning pink and black swirled rock, and very commonly used for head stones. Commercially known as ‘Rainbow granite', it is the oldest building stone you’ll find in the country, and perhaps the entire world. But, it isn't granite- many building stones carry inaccurate geologic terms. You can see Morton Gneiss in buildings all over the US: the Exchange Building in downtown Seattle, the West Publishing Building in St. Paul, the Banker's Life Insurance Building in Des Moines, the Adler Planetarium in Chicago, the Oklahoma Natural Gas Building in Tulsa, the Old State Library in  Richmond, Virginia, Baltimore's Police Headquarters, and the AIG Building in New York. It is distinctive and once you are familiar with the rock's appearance, you may find it somewhere in your town. If you do, contact me via email and send a photo. tuckerd@geol.wwu.edu.
 
Learn more about the Morton Gneiss and see photos of cut rock used as building stone on my friend David Williams' website, 'Stories in Stone'. David is the author of Stories in Stone- Travels through Urban Geology which describes building stones used in the US and their origins all over the world. And here is another great website that describes and photographs the quarry operations.