38 SMITHSONIAN INSTITUTION 



Regardless of its origin, two seasons' work has developed the fact 

 that this fossil bone deposit is one of the important discoveries in the 

 field of vertebrate paleontology of recent years. The outcome of these 

 operations by the Smithsonian Institution parties has been most grati- 

 fying. As already stated the principal yield of the deposit consists of 

 abundant remains of a hitherto unknown species of horse belonging to 

 the rare genus Plesippus, an animal which stands directly intermedi- 

 ate between the horses of the Pleistocene and present day, and the 

 three-toed kinds of still more ancient time. The material collected from 

 this deposit in the two seasons includes more than 40 more or less 

 complete skulls and sufficient bones of other parts of the body to 

 restore at least three or four entire skeletons. The bones collected 

 represent all stages of growth of both sexes from embryo to old age. 

 Thus they afford an unusual opportunity for a systematic study of 

 the species, especially in reference to the limits of individual and sex 

 variations. 



Other fossil remains found associated with the much more abundant 

 horse material were those of a large beaver, an otter, a mastodon, a 

 large peccary, a rodent of the muskrat group, a frog, a swamp turtle, 

 and a small fish. From exposures of the same formation in the gen- 

 eral vicinity were also collected remains of these and additional extinct 

 species of mammals, the latter including several species of rodents, a 

 large cat, two species of camel, and a small ground sloth. These, 

 together with the animal remains of the fossil bone deposit, when 

 studied, will give rather definite evidence regarding the true age of 

 this mass of sedimentary accumulation to which has been given the 

 name Idaho formation. This formation has hitherto been regarded 

 by some authorities as belonging to the Pleistocene, or so-called Ice 

 Age, and by others as representing the upper member of the next older 

 geologic period, the Pliocene. The preliminary study of the fossils 

 collected by our party in the Hagerman locality seems strongly to favor 

 the placing of their age as Upper Pliocene. This marks their time of 

 deposition as not less than a million years ago. 



To the fossil hunter such a deposit as the one here described is of 

 much more than passing interest. First there is a satisfaction in work- 

 ing out a successful technique for collecting and preparing the bones 

 for shipment to the laboratory ; and there is the added keen pleasure 

 of anticipation and expectation, as foot after foot and yard after yard 

 of undisturbed ground is worked over, that the next bone to be dis- 

 covered and developed will prove to be new to science or at least a 

 better specimen than has before been found of an already known 

 species. Such collecting also has its monotonous and prosaic side. At 



