526 PROCEEDINGS ()F THE WASHINGTON MEETING 



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 German}', he was much impressed with 

 the methods of marking the separate horizons by means of some char- 

 acteristic fossil. He believed the vertebrates were the most sensitive 

 time-markers, and therefore endeavored to determine and limit geolog- 

 ical horizons wholly by fossil vertebrate remains. The inherent fault 

 of this system is that the vertebrates are not always the most highly dif- 

 ferentiated 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. Geological facts will be found scat- 

 tered through many of his publications dealing principally with fossil 

 vertebrates. One of the latest problems to interest him was the age of 

 the series of variegated clays extending from Marthas Vineyard south 

 along the Atlantic coast into Maiyland. His investigations led him to 

 refer them to the Jurassic, a formation which had been considered as 

 absent in eastern North America. 



There yet remains for consideration the real work of his life, hia pub- 

 lications on the fossil vertebrates, and it is at once evident, from a glance 

 at his bibliography, that his chief researches w T ere upon the reptiles, 

 birds, and mammals. There are three papers on fossil fishes, contain- 

 ing notices of several new forms, but no real research in this class was 

 ever undertaken by him. The amphibians also claimed but little at- 

 tention, and his observations on the metamorphosis of the recent Siredon 

 into Amblystoma and two brief notices of amphibian footprints in the 

 Devonian and Carboniferous comprise the whole. 



It is with extreme hesitation and a sense of inadequacy that the 

 writer ventures to review, even in the briefest and most superficial man- 

 ner, the work which undoubted^ constitutes the literary essence of his 

 life-work. Future investigators alone can criticall}^ estimate the great 

 mass of facts which Marsh brought out and which he wove into the de- 

 partments of fossil reptiles, birds, and mammals. 



His most comprehensive work, and in many ways the most masterly, 

 is the address delivered before the American Association for the Ad- 



