R. L. Moodie — Mason Greek Shales. 285 



The paleogeographic conditions of the beds containing the 

 Amphibia at Mazon Creek, as well as those at Twin Mounds, 

 are well represented in Doctor Schuchert's map.* A refer- 

 ence to this map, that of the Upper Pennsylvanian times, will 

 show that the Mazon Creek deposits and the Twin Mounds 

 deposits occur on the margin of the heavily shaded portion of 

 the Upper Pennsylvanic sea. Doctor Schuchert suggests that 

 the Twin Mounds beds represent a peninsula or a small island 

 near the shore during Pennsylvanic times. 



So far as our knowledge goes there is no evidence of verte- 

 brate life of the uplands at this time. It was confined to the 

 waters and to the borders of the waters. To be sure, we know 

 very little of upland deposits, bat there should be some sug- 

 gestion of the vertebrates did they occur. It is a matter of the 

 profoundest interest to witness here in the Upper Pennsylvanian 

 the appearance of the earliest types of that branch of the ani- 

 mal kingdom which, in later epochs, was to dominate the entire 

 world, some of these types returning to the water as a second- 

 ary adaptation. It is not possible for us to examine these lowly 

 organized creatures without thin kino; that in them, or in 

 creatures like them, lay the possibilities for the development 

 of that race of animals to which we ourselves belong. Dr. 

 Jennings has recently + expressed this idea, approaching the 

 subject from an entirely different point of view when he says : 

 "I was in actual material existence as a living organism, and 

 indeed thousands or millions years old, when the pyramids 

 were built, ..." Is it possible for us to conceive that the 

 habits of these amphibian creatures of the Mazon Creek 

 region have left an impress on our own characters i If so, are 

 they not worthy of our very careful attention ? 



Just what the details of the mode of evolution from these 

 small creatures may have been we do not yet know, but patient 

 and faithful search will reveal many new facts of the profound- 

 est importance. 



The University of Kansas, Lawrence, Kansas. 



* Plate 84, Paleogeographv of North America. Bull. Amer. Geol. Soe., 

 xx, 1910. 



\ Science, X. S., xxxiv, p. 904. 



