PREFACE. 



1. Sources of Collections. — The localities which yielded the fossils 

 described in the following pages are the following : 



In 1872 I conducted an exploring party in Southwestern Wyoming. 

 I left Fort Bridger July 19, and followed the road to Cottonwood Creek, 

 southeast eighteen miles, whence we made our first excursions into the bad 

 lands. After this our route laid along Cottonwood Ci'eek to Smith's Fork 

 of Green River, thence along Black's Fork, and thence to Green River City. 

 We then followed Bitter Creek to Black Buttes, and, leaving the line of the 

 Union Pacific Railroad, ti-aveled south toward the headwaters of the Ver- 

 million. Before reaching this point we explored the Mammoth Buttes, which 

 form the water-shed between South Bitter Creek and Vermillion, and ex- 

 amined the bad lands of the Washakie Ba.sin carefully. In reaching this 

 point we crossed a portion of the Cretaceous formation, and I took especial 

 pains to determine the relations of the strata at these points. 



We returned from this region and struck Green River seventeen miles 

 above Green River City. We proceeded northward to the mouth of La- 

 barge Creek, and, returning a short distance, ascended Fontanelle Creek to 

 near its source in the outlying ranges of the Ham's Fork Mountains. The 

 relation between the lake-deposits and the older strata here claimed special 

 attention. We then descended Ham's Fork to the Union Pacific Railroad 

 and returned to Fort Bridger. 



Special expeditions were made to the region round Evanston, and to 

 Elko, Nev., with gratifying success. 



We obtained, in round numbers, one hundred species of vertebrated 

 animals of the Eocene period, of which about sixty were new to science. 

 We obtained material for the addition of two orders of mammals to those 



