This represented one of the most interesting finds to my mind. It appears to be the foot of a bivalve, possibly a razor clam. This is not an impression, but is the actual fossilized flesh of the creature. For it to be preserved like this, it would have to have been quickly buried in an anaerobic environment as a result of some catastrophic event like, for instance, the flood of Noah's day.
Another common fossil were these pieces of finger coral.
Another sample of a similar "rock." It has the same general shape as the previous picture, but this view shows it from the end.
I could go one showing fossils for several more days. If it has whetted your appetite and you live in the Calvert County area, you may want to see the collection of fossils at the Calvert Marine Museum that were (mostly) found at Calvert Cliffs. This is one last "cave painting-type" image of the stream bed. Who knows how many fossils are yet to be revealed there.