Proceedings of the Ohio State Academy of Science 35 



tailed paleontologic work has been done in this country. De- 

 scription of new species has been an insignificant part of the 

 work. It has concerned rather faunas, the comparison of faunas 

 of different regions, and the movements or migrations of faunas. 

 This has also required study of the rocks in which the faunas 

 were found, and the use of all possible means to determine areas 

 of past seas, and barriers to and lines of migration. The study 

 of the geography of the past has always been a part of geology, 

 but in recent times the subject has assumed so much importance 

 that it has received the dignity of a name of its own, and we now 

 have paleogeography, paleogeographers. and paleogeographic 

 maps of the dififerent geological periods. Two recent works of the 

 highest value summarize what has already been done, and form 

 the basis from which all work in the near future must be built. 

 These are Schuchert's PaleogeograpJiy of North America (1908) 

 and Ulrich's Revision of the Paleozoic Systems (1910). 



Schuchert's paper gives an unrivalled series of paleo- 

 geographic maps of North America. Both papers discuss in de- 

 tail the principles of paleogeographic interpretation and their ap- 

 plication to American formations. They give in far greater de- 

 tail than has been given before the behavior of the continental 

 surface in geological time; the advances and retreats of the sea, 

 and the shiftings of areas of erosion and sedimentation. One 

 important result of this work is to change somewhat the idea 

 which was current a couple of decades ago in regard to con- 

 tinental growth, especially the growth of the American continent. 

 It was Dana's belief that there had been a sort of evolution of the 

 North American continent from the middle or later Cambrian, 

 when the present continental surface was largely submerged, ex- 

 cept for land areas in Canada, along the crystalline area of the 

 Appalachians and in the west, to the present condition of con- 

 tinental emergence. Not of course a steady progress, rather a 

 progress with relapses ; and yet after each great period of 

 geological revolution a nearer approach to present conditions. Re- 

 cent stratigraphic studies indicate no such progress : instead, at 

 different times, some later and some earlier even than the begin- 

 ning of the Paleozoic, land area was as great if not greater than 



