GEOLOGIC THEORY AND METHOD 263 



Eosebud (Lower Miocene), South Dakota. Matthew and Gidley, 1904. 

 Virgin Valley (Middle Miocene), N'evada. Merriam, 1910. 



PLIOCENE 



Rattlesnake (early Pliocene), Oregon. Merriam, 1901. 



Snake Creek (Lower Pliocene), Nebraska. Matthew and Cook, 1909. 



Thousand Creek (Lower Pliocene), Nevada. Merriam, 1910. 



PLEISTOCENE 



Rock Creek = Sheridan (Pleistocene), Texas. Gidley, 1904. 



Many of the names proposed either have been or will be retained as 

 the designations of epochs in the standard time scale for the non-marine 

 Tertiary. They represent both the discovery of entirely new fossiliferous 

 horizons and the subdivision of previously known formations necessi- 

 tated by a fuller knowledge of the faunas contained therein. 



Correlation studies have kept pace with the naming and characteriza- 

 tion of new horizons. In Osborn's "Age of Mammals" (1910) we have 

 a remarkably complete and satisfactory summary of all that is known to 

 date of the faunal and time relations of the mammal-bearing beds of 

 Europe and North America. Less progress can be reported in the corre- 

 lation of marine with non-marine Tertiary formations. In North Amer- 

 ica, the Atlantic border region holds out little promise for the future 

 except, perhaps, in Florida, but on the Pacific side, even though the 

 whole problem of the relation of the epicontinental formations east of the 

 Sierra Nevada to the marine deposits of the coast region is far from a 

 definite settlement, the discovery of fragmentary mammalian remains of 

 late Miocene to Pliocene age in the largely marine Jacalitos and Etchegoin 

 formations of the western San Joaquin Valley and of a mammal-bearing 

 Upper Miocene horizon in the Mohave Desert suggest that, ultimately, 

 correlations may be established. In South America, where marine beds 

 are interstratified with non-marine formations affording vertebrates, 

 much may be hoped for, but so far there has been fundamental difference 

 of opinion between Argentinian geologists and paleontologists and the 

 rest of the geological world, the former contending for a greater age for 

 their fossiliferous formations than northern workers are disposed to 

 admit. It seems to be positively established that dinosaurs and mam- 

 mals occur in the Notostylops beds. The mammals are not like those 

 known elsewhere from the Cretaceous, but are of highly advanced type, 

 comparable to those of the Puerco Paleocene of North America. Either 

 we must admit that dinosaurs existed during the Tertiary in South 



