Fig. 3. Block diagram illustrating dip and strike.
STRIKE DIRECTION ROCK LAYER SURFACE (PLANE) LAKE LEVEL HORIZONTAL DIP ROCK LAYER
Search the top of a few layers and you will notice many shell and other animal impressions. Do they represent animals which lived hundreds of millions of years ago or were they washed onto these rocks from present-day Lake Champlain? If you try to make a collection of the shell impressions you will see that they are a part of the rock and therefore must represent remains of animals that were buried in the ancient lime muds. These preserved remains[3] are called fossils. The geologist who specializes in the study of fossils is called a paleontologist. You may ask, “What can fossils tell me about the past?” In the first place, fossils tell us at what time in the past the sediments in which they are found were deposited. In this way, the relative age[4] of the rock layers found in the Park can be learned. Secondly, the environment or surroundings in which these ancient sediments were deposited can be reconstructed from the types of fossils contained within them. Certain animals living today are quite similar to those in the Park rocks and their environment in today’s sea can be used to reconstruct the environment of animals which lived in the past. The characteristics of the rocks and their relation to adjacent rocks are considered in any reconstruction of past environment. In the third place, the study of fossils is a mainstay of the theory of evolution. That is to say, changes in fossil forms collected from groups of successively younger rock layers document the theory that life has evolved little by little since its first appearance on Earth. Finally, it should be mentioned that some animals found as fossils are not living today and have not lived, to the best of our knowledge, for millions of years. Why did these forms of life die out? What set of circumstances led to their extinction? The answers to these questions are not easy to find and they are highly speculative.
Fig. 4. Standard Geologic Time Scale.
| GEOLOGIC TIME | |||
|---|---|---|---|
| ERA | YEARS AGO | PERIODS | EVENTS |
| CENOZOIC | 70,000,000 | CENOZOIC | MAN (1½ MILLION) |
| MESOZOIC | 125,000,000 | CRETACEOUS | END OF DINOSAURS |
| 165,000,000 | JURASSIC | FIRST BIRD | |
| 200,000,000 | TRIASSIC | FIRST DINOSAUR | |
| PALEOZOIC | 230,000,000 | PERMIAN | END OF TRILOBITES |
| 260,000,000 | PENNSYLVANIAN | ||
| 290,000,000 | MISSISSIPPIAN | ||
| 330,000,000 | DEVONIAN | ||
| 360,000,000 | SILURIAN | ||
| 420,000,000 | ORDOVICIAN | ROCKS OF D.A.R. STATE PARK | |
| 500,000,000 | CAMBRIAN | ||
| BEGINNING OF FOSSIL RECORD | |||
| 1 BILLION | |||
| 2 BILLION | |||
| 3 BILLION | |||
| 4 BILLION | |||
| PRECAMBRIAN | |||
THE FOSSILS
Many groups of invertebrates are represented in the fossils of D.A.R. State Park. [Plate 1] will help you to identify these fossils. The name, phylum (major group) and age of each fossil are provided in the explanation of the plate. The following paragraphs describe each phylum represented in the Park rocks.
