In the study of fossils there are two important field aids usually
available. For any locality there should be a geological map and a
section showing the sequence and character of the strata. On a
small-scale map many of the local details have to be omitted, but the
position of the larger exposures is indicated and, with this information
at hand, the fossil-bearing strata may be located with the help of a
geological section. The latter is frequently obtained from technical
reports published by State and National Geological Surveys. Frequently,
however, it is possible to obtain only a general plan for a given
locality, and a great deal of literature may have to be scanned in order
to get that. Excellent geological maps of Colorado have been published
by the Colorado Geological Survey and the United States Geological
Survey.
It often happens that a formation is not where we expect to find it,
this being due to several possible factors. The sediments may not have
been deposited there, or they may have been removed by erosion. Where
the structure has been disturbed by folding and faulting, a multitude of
complications is introduced. The expected sequence is sometimes inverted
and repeated through a series of folds. Formations also may be moved
miles out of place by faulting. Both thickness and character of
sediments may vary considerably within a formation. In some regions the
geology is very simple, in others extremely difficult to understand.
[Illustration: FORMATIONS of the DENVER-FOOTHILLS REGION
A GENERALIZED SECTION SHOWING SOME OF THE SURFACE FEATURES
RED BEDS HOGBACKS TABLE MOUNTAIN DENVER DISTRICT