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Fossils: the remains or impression of a prehistoric organism preserved in petrified form or as a mold or cast in rock. (Oxford)

  Imagine...400 million years ago, before the present Rocky Mountains were up. They say it was a shallow, calm sea that extended from present day Canada to the gulf. Corals are the shape of communities of little creatures. Millions of tiny creatures over millions of years. The land rose up, the sea drained away and today, (where it hasn't been plowed up), you can find fossilized sea floor. The fossils are silica which is why they last.

Fossils, Fossil Molds, Interior Casts


Identification Sources:

The Audubon Society Field Guide to North American Fossils.

Geological Survey of Wyoming- Paleontology of the Green River Formation. Bulletin 63

Dinosaur Valley State Park, Glen Rose Texas.

Firefly Guide to Minerals Rocks and Fossils.

Geology of the San Francisco Bay region.

Geology of the Sierra Nevada.

key:
1. Pre-Cambrian  Eon .57-.70 billion yrs.
2. Cambrian Period 570-500 million yrs.
3. Ordovician Period 500-430 million yrs.
4. Silurian Period 430-395 million yrs.
5. Devonian Period 395-345 million yrs.
6. Mississippian Period 345-325 million yrs.
7. Pennsylvanian Period 325-280 million yrs.
8. Permian Period 280-225 million yrs.
9. Triassic Period 225-190 million yrs.
10. Jurassic Period 190-136 million yrs.
11. Cretaceous Period 136-65 million yrs
12. Paleocene Epoch 65-54 million yrs.
13. Eocene Epoch 54-37.5 million yrs.
14. Oligocene Epoch 37.5-26 million yrs.
15.  Miocene Epoch 26-5 million yrs.
16. Tertiary Period 5- 1.8 million yrs.
17. Pleistocene Epoch 1.8 million -11,000 yrs.
18. Quaternary Period 11,000 yrs. to Present.