.160 EEPOET UNITED STATES GEOLOGICAL SURVEY. 



ing tlie Wasatch Eange at its junction with that of the Uintas, to Great 

 Salt Lake, the most westerly point of my travel. Eecrossing the Wasatch 

 upon the north side of the junction of the two ranges, I proceeded east- 

 ward, my general course lying between the northern base of the Uintas 

 and the Union Pacific Eailroad, and finally leaving the field on October 

 1, at Eawlins Station on that railroad. 



Aside from accomplishing the special objects of the journey here out- 

 lined, I was enabled to spend considerable time in the district between 

 Yampa and White rivers, making essential additions to the geological 

 studies I had made there during the previous season, the results of which 

 have been incorporated into my rei)ort for 1876, now in type. 



In the discussions of the strata and fossil faunae of each of the locali- 

 ties which I visited during this season, as well as in the more general 

 discussions at the close of this report, I have made use not only of much 

 information that I have obtained by former similar field labors, but also, 

 for purposes of comparison, of much that has been done and published 

 by others. Therefore the scoi)e of this report is much greater than the 

 results of the single season's labor in the field for 1877. Among this 

 added material are some lists of fossils which have from time to time 

 been sent to the office of the survey, by persons not officially connected 

 with it, from various and distantly-separated localities in the western 

 part of the national domain. By the use of these, in connection with 

 other information, I i3resent some interesting and important facts con- 

 cerning the geographical distribution of invertebrate tyjDcs, especially 

 during the Cretaceous i)eriod. 



While this season's work is seen to be only the beginning of a neces- 

 sary series of similar field investigations, it is a matter for congratula- 

 tion that so good a degree of progress has been made in the elucidation, 

 upon the basis estabMshed as the result of your eafly labors in the west- 

 ern field, of the questions which they involve. 

 Very respectfully, yours, 



C. A. WHITE. 



Prof. P. Y. Hatden, 

 In charge of the United States Geological Survey of the Territories. 



