Hoover Point - Green Coolness EarthCache
Hoover Point - Green Coolness
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This road cut at Hoover Point overlook is a fascinating specimen of gelogic study, but we will focus on the green glauconitic Cambrian sandstone (trilobite hash) of the roadcut.
Park at the scenic overlook and gaze at the Colorado River, Lake Lyndon B. Johnson reservoir and the ancient rocks of the Llano uplift. You're looking at precambrian rocks (570 - 4,500 millions of years old!). But this Earth cache is about what lies behind you - turn around and behold a Central Texas wonder. Please do not cross the highway. It is dangerous. All questions can be answered by standing where you are and simply taking in the spectacular, colorful roadcut. We will be focusing on the lower, green/black layers of the roadcut, glauconitic Cambrian sandstone.
1. Age. As opposed to the preCambrian rocks in the far distance, these rocks are newer, Cambrian rocks which are only 505 to 570 million years old.
2. Composition. Trilobites were ancient jointed-leg, segmented creatures. (Think roly-polys.) "The green color of the sandstone is due to the mineral glauconite, an iron-rich mineral deposited in shallow marine waters commonly as fecal pellets of ocean organisms. The trilobites and glauconite thus place the deposition of this Cambrian sand in shallow marine seas." Spearing, Darwin. Roadside Geology of Texas. Missoula, MT: Mountain Press Publishing Company, 1991. 173-174. Print.
3. Coolness aspect. Geologists from all over the world visit our Llano uplift (Enchanted Rock), and visit this roadcut also. How cool is that?
To receive credit for this Earth cache, anaswer the following questions (send an email to the cache owner, do not encrypt on this page):
1. How many distinct layers of glauconite do you see as you look across the highway at the roadcut? This can be difficult - focus on the larger bands of green sandstone for your answer.
2. Estimate the height of the lowest layer of glauconite, and give your answer in proper SI. (This layer has big white round rocks in it called concretions.)
2. If the deposits of the glauconitic sandstone represent a shallow, marine environment, how the heck did all those roly poly carcasses and fish poop get to the top of this mountain?
3. If you could taste the green sandstone, do you think it would taste like salt because it's made up of ancient sea creatures and their excrements? (Many, if not all, geology professors who lead field trips to this amazing place ask their students to taste the fish poop!) Please defend your answer.
(visit link)
4. Stand at GZ with your back to the road cut. Look towards the right, at about 2 o'clock. What do you see?
5.Please share any photos you take of the roadcut WITHOUT giving the answers, please! (visit link)
Additional Hints
(Decrypt)
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