A GREAT PERMIAN DELTA 557 



A GREAT PERMIAN DELTA AND ITS VERTEBRATE LIFE, 

 WITH RESTORATIONS BY THE AUTHOR 



By Dr. E. C. CASE. 



ASSISTANT PROFESSOR OF HISTORICAL GEOLOGY AND PALEONTOLOGY, 

 UNIVERSITY OF MICHIGAN 



AS early as 1878 it was known that the remains of a wonderful 

 group of animals lay hid in the rocks of north central Texas, 

 that had lived their appointed time and passed away before the earth 

 history was half completed; since then collectors have gone into this 

 region more or less regularly, contending in the early days with hostile 

 Indians and later with bad water and difficult transportation. Since 

 1895 the author has made several trips, gathering vertebrate fossils for 

 the University of Chicago and the American Museum of Natural 

 History in New York. The descriptions below are based on these 

 collections and those of earlier workers. 



Perhaps one can get the best idea of the age of the rocks and the 

 fossils by remembering that they were laid down in the portion of 

 geological time called the Permian age, just after the period of the coal 

 deposition. Reckoning the completed history of the earth as about 

 one hundred millions of years, these rocks and fossils are from thirty 

 to forty millions of years old. At the beginning of the Carboniferous 

 age, when the coal was laid down, the part of the continent that is 

 now called the Mississippi- Valley was covered by a wide sea, but 

 during this age there was a progressive shallowing which culminated 

 in the elevation of the Appalachian mountains in the east and the 

 appearance of dry land from the new mountains on the east to the 

 forebears of the Rockies on the west. 



The appearance of dry land was at once the cause of the develop- 

 ment of the wonderful group of Permian animals and the reason that 

 so few are preserved to us, for it is only when the hard parts of animals 

 or plants are buried in some water-soaked layer of the earth or are 

 covered by water that they can be petrified and preserved. If they re- 

 main exposed to the air they are soon destroyed; so, of the skeletons 

 of the thousands of buffalo left lying on the plains but a few years ago, 

 there remain to-day but a few rotten and frost-split horns and bones. 

 Undoubtedly in the muddy banks and bars of the rivers there are skele- 

 tons undergoing the slow process of petrifaction which will preserve 

 them to be the chief treasure of some future museum. And so be- 

 cause of the land conditions which prevailed over so much of the 



