What Makes it Hard to Identify Fossils?
Compaction of sediment. Clay muds compact more than lime muds. Consequently, fossils preserved in shale commonly are flattened, their shells cracked and or broken. Fossils preserved in limestone, on the other hand, often retain their original shape and convexity, and are not flattened at all. Sometimes flattened and nonflattened individuals of the same species have been described as different species.
