For the more minute correlations in stratigraphy no group of fossils is of more practical service than the echinoderms. Where the remains of these organisms are abundant, as in many of the Paleozoic rocks, the entire history of events may be inferred from them alone. Composed of hard parts or plates which are more or less regularly shaped and which are arranged according to a definite plan the evolution of the various forms may be readily traced and the slightest changes in physical conditions at the time of sedimentation quickly detected. In the Mississippi basin the crinoids are widely distributed both geographically and geologically in the later Paleozoic strata. Their structure has been made out in great detail and hence their value for geological classificatory purposes is second to no other criteria. The same is also true of a closely related class of stemmed echinoderms - the blastoids.
Proceedings of the Iowa Academy of Sciences
©1894 Iowa Academy of Science, Inc.
Keyes, Charles Rollin
"Synopsis of American Paleozioc Echinoids,"
Proceedings of the Iowa Academy of Science, 2(1), 178-194.
Available at: https://scholarworks.uni.edu/pias/vol2/iss1/39