Othniel Charles Marsh. 415 



published nothing in this department. Two papers presented 

 some Annelids considered as new, from the Jurassic of Ger- 

 many. Another showed the origin of the double lobe-lines in 

 Ceratites. His papers on American invertebrates comprised a 

 description of a new genus of Fossil Sponge fBrachiospongiaJ, 

 a new form of Crustacean Trail from the Potsdam Sandstone, 

 and a note on color markings in Endoceras. He also showed 

 that Palceotrochis and Lignilites were not of organic origin, 

 though the contrary had been previously supposed. 



In the domain of Geology, his chief interests lay in the 

 formations from which he secured important series of fossil 

 vertebrates. Probably his greatest geological discovery was 

 the Uinta Basin, an Eocene deposit of the eastern Uinta 

 Mountains. It was first visited in 1870. Having studied most 

 of the Tertiary lake basins in the Rocky Mountain region, he 

 gave, in 1875, a synopsis of their geological features. As a 

 natural result of studying Geology in Germany, he was much 

 impressed with the methods of marking the separate horizons 

 by means of some characteristic fossil. He believed the verte- 

 brates were the most sensitive time-markers, and therefore 

 endeavored to determine and limit geological horizons wholly 

 by fossil vertebrate remains. The inherent fault of this sys- 

 tem is that the vertebrates are not always the most highly 

 differentiated and specialized types in any given fauna, and it is 

 these qualities alone that can be safely employed in organic 

 chronometry. This method is usually of great value in fresh- 

 water deposits rich in vertebrate remains, but it can be seldom 

 used to advantage in marine sediments or in formations 

 containing a scanty vertebrate fauna. Thus, while the name 

 Equus Beds is very appropriate for a horizon in the Pliocene, 

 on account of the abundance of remains of fossil horses, the 

 same cannot be said of the term Eosaurus Beds as an equivalent 

 of the entire series of the Coal Measures, especially as but two 

 vertebrae of this animal have ever been discovered. Geolog- 

 ical facts will be found scattered through many of his publica- 

 tions dealing principally with fossil vertebrates. One of the 

 latest problems to interest him was the age of the series of 

 variegated clays extending from Martha's Yineyard south along 

 the Atlantic coast into Maryland. His investigations led him 



