Tag Archives: geology
One of my favorite places in the whole world is along the Clark Fork River in Paradise, Montana. When we drove to Bigfork the other day, we had the good fortune to see the Prichard Formation
on a perfect day. Turquoise water in the foreground and deep red-rust hues in the background. The Prichard Formation is 1.5 billion years old and the outcrop in the photo is called an overthrust belt. Jutting up from the earth at an angle, it is among the oldest exposed rock in Montana. Why do I like it? My grandfather, who lived in Central Oregon, taught me to be a rock hound at an early age. It was at his behest that I started collecting minerals. He gave me some fine specimens. He also lived very close to the John Day Fossil Beds and the painted hills. There was a mountainous rock across from his compound on the Ochoco Reservoir. My brothers and I could scramble, hunt for rocks, and see bats hanging upside down. So, when I see the big lump of rock on the other side of the Clark Fork, I feel at home. The Prichard Formation extends over a wide area…the part you see here is only a fraction. The bottom of it is so deep, it’s never been found. “The Prichard formed as layer upon layer of sand, silt and clay was deposited from a river delta into a sea covering parts of what is now Montana, Idaho, Washington and Canada,” according to the Lolo National Forest historical marker “Over millions of years, heat and pressure turned the sediments into a hard, metamorphic rock, argillite.” If you are interested in scientific information about this geological wonder, click here to read Dinochick Blogs (billed as “Random Posting on Geology and Paleontology with a bit of spunk and sass thrown in.”) Below, the National Park Service information graphic shows that the Prichard and Altyn Formations are underneath all other masses in Glacier National Park.
Earlier today, I was thinking about clay…how it is strengthened when molecules overlap. This lead to pondering the organic material itself. I’ve always been curious about how things work and this tendency led to an interest in scientific processes. So, after looking at a few sites, I came across a description about the formation of clay in entry on the Absolute Astronomy site. It included everything I needed to know. Basically, clay is created when rocks weather over long periods of time, which makes chemical changes happen. According to the entry, rocks with silica eventually create “low concentrations of carbonic acid and other diluted solvents. These solvents, usually acidic, migrate through the weathering rock after leaching through upper weathered layers.” It said that slowly forming clays present in two ways, either as a “residual deposit” or, if we’re talking about thick clay formations, then by the sedimentary process after erosion and movement shifts it from its “original location of formation.” Clays are also found in marine environments, near big lakes or by “marine deposits.” This would explain why there is so much naturally occurring clay in my area, at the end of the Burrard Inlet in Metro Vancouver. Many creeks feed into the inlet. Just on my street, alone, five creeks intersect the four-block long lane, then head downhill to the ocean. There has been much ancient and modern-day mudslide activity here. It has left big boulders and large river-type stones above and below ground here. Ocean water is four blocks away, at present, but I don’t know where the waterline was in ancient times. Back to clay, though. Evidently, kaolin is formed on the spot, but other clays have moved by way of water and erosion. A type of clay is determined by different ways of grouping and categorizing. This source says there are up to four main types:
- Chlorite (sometimes considered a phyllosilicate)
Apparently, these are further broken down into some 30 odd pure clays, but the entry says that natural clays are most often a combination. Further description states that varve is clay that shows “visible annual layers” formed as the result of seasonal changes and that it is commonly found in former glacial lakes, which it says have very little movement. As I read about clay on this site, I was particularly interested in a unique type of clay called quick clay, which is a “marine clay indigenous to the glaciated terrains of Norway, Canada, Northern Ireland and Sweden. It is a highly sensitive clay, prone to liquefaction, which has been involved in several deadly landslides.”
In any event, I answered my initial question…how is clay created in nature? I am satisfied with what I learned and if I want to investigate further, I have several avenues….