232 A CENTURY OF SCIENCE 



tain so much material that it has not yet entirely seen 

 the light of scientific exposition. Marsh's first trip to 

 the West was in 1868, the first formal expedition being 

 organized two years later. These expeditions, of which 

 there were four, were privately financed except for the 

 material and military escort furnished by the United 

 States Government, and consisted of a personnel drawn 

 entirely from the graduate or undergraduate body 

 of Yale University. These parties explored Kansas, 

 Nebraska, Wyoming, Utah, and Oregon, and returned 

 laden with material from the Cretaceous and Tertiary 

 formations of the West. Some of this is of necessity 

 somewhat fragmentary, but type after type was secured 

 which, with his exhaustive knowledge of comparative 

 anatomy, enabled Marsh to announce discovery after dis- 

 covery of species, genera, families, and even orders of 

 mammals, birds, and reptiles which were unknown to 

 science. The year 1873 saw the last of the student expe- 

 ditions, and thereafter until the close of his life the work 

 of collecting was done under Marsh 's supervision, but by 

 paid explorers, many of whom had been his scouts and 

 guides in the formal expeditions or had been especially 

 trained by him in the East. In 1882, after fourteen years 

 of the experience thus gained, Marsh was appointed verte- 

 brate paleontologist to the United States Geological Sur- 

 vey, which relieved him in part of the personal expense 

 connected with the collecting, although up to within 

 a short time of his death his own fortune was very 

 largely spent in enlarging his collections. After his con- 

 nection with the Survey was established, Marsh had two 

 main purposes in view in making the collections : (1) to 

 determine the geological horizon of each locality where 

 a large series of vertebrate fossils was found, and (2) to 

 secure from these localities large collections of the more 

 important forms sufficiently extensive to reveal, if possi- 

 ble, the life histories of each. Marsh believed that the 

 material thus secured would serve as key or diagnostic 

 fossils to all horizons of our western geology above the 

 Paleozoic, a belief in which he was in advance of his time, 

 for few of his contemporaries appreciated the value of 

 vertebrates as horizon markers. The result of the ful- 

 filment of his second purpose saw the accumulation of 



