TEE FALEONTOLOGIC RECORD 59* 



than are recognized for invertebrates, because of the scattered nature of 

 the material and the additional probability that continental deposits, in 

 which alone vertebrates have their chief importance as guide fossils, 

 have accumulated more rapidly than marine beds. Similarly, condi- 

 tions peculiar to their mode of deposition make it difficult, perhaps 

 impossible, to define lithologically the limits of the zones we are at- 

 tempting to characterize. And here another trouble confronts us, for 

 the faunas are incompletely known, and we are not yet in a position to 

 dogmatize too freely on the subject of vertebrate index fossils. But 

 that the method of zonal studies is the correct one is very clearly shown 

 in Dr. Matthew's 2 recent monograph on the Carnivora and Insectivora 

 of the Bridger Eocene, and will be demonstrated with equal force when 

 Professor Osborn's volume on the titanotheres is published. 



Various attempts have been made at the correlation of European 

 and American mammal horizons, their measure of success depending 

 entirely on the degree of closeness with which these correspond to 

 true zones. At present, we are attempting to correlate subdivisions, 

 both faunal and stratigraphic, of all orders of magnitude, the majority 

 including many faunules and many zones. Evidently, this tendency 

 must be corrected by careful zonal studies, if vertebrate paleontology 

 is to have any standing as an aid to stratigraphy in the correlation of 

 our non-marine formations. 



BIOLOGIC PKINCIPLES OF PALEOGEOGRAPHY 



By Professor CHARLES SCHTJCHERT 



TALE UNIVERSITY 



IN deciphering the ancient geography as to the position of the marine 

 waters and the land masses, we as pioneers in this work must be 

 controlled primarily by the known fossilized life and secondarily by 

 the character and place of deposition of the geologic formations. This 

 record is most extensive and best preserved in the deposits of the con- 

 tinental and the littoral region along the continental shelves of the 

 oceanic areas. Back of these two principles, however, there is another 

 that eventually will become the primary guiding factor. It is the prin- 

 ciple of diastrophism — one seeking to explain the causes for the 

 periodic movements of the lithosphere. 



In our study of the ancient seas with their sediments and entombed 

 life we have safe guidance in the phenomena of the present. Ludwig 

 in 1886 estimated the species of animals then known to naturalists as 

 upwards of 312,000, and in 1905 Stiles thought this great total had 

 increased to about 470,000 forms. Of this sum fully 60 per cent, are 

 insects, and of the remainder, the writer concludes that about 25 per 



J Memoirs American Museum of Natural History, Vol. IX., Part VI., 1909. 



