LETTER TO THE SECRETARY. XVII 



side, and making comparisons of both their lithological and paleonto- 

 logical characteristics. 



In this way he traversed the whole length of the Uintah Range, cross- 

 ing at its junction with the Wasatch Range over into the valley of Great 

 Salt Lake. Eecrossing the Wasatch to the north side of the Uintah 

 Range, he continued his examinations of the Cretaceous and Tertiary 

 strata into and entirely across the great Green River Basin, leaving the 

 field at the close of the season at Rawlins Station, on the Uuion Pacific 

 Railroad. 



A general statement of the results of the season's work has been 

 given in a previous paragraph, but the following additional summary 

 will make the statement somewhat clearer, being made after the route 

 of the season's travel has been indicated. The formations of later 

 Mesozoic and earlier Cenozoic ages, especially those to which Dr. White, 

 in former publications, has applied the provisional designation of "Post- 

 Cretaceous," have received particular attention. The extensive explora- 

 tions of Dr. Hayden in former years, and the paleontological investi- 

 gations of the late Mr. Meek, pointed strongly to the equivalency of the 

 Fort Union beds of the Upper Missouri River with the lignitic formation 

 as it exists along the base of the Rocky Mountains in Colorado, and 

 also to the equivalency of the latter with the Bitter Creek series west 

 of the Rocky Mountains. The investigations of this year have fully 

 confirmed these views by the discovery not merely of one or two doubt- 

 ful species common to the strata of each of these regions, but by an 

 identical molluscan fauna ranging through the whole series in each of 

 the regions named. 



This shows that the strata just referred to all belong to one well- 

 marked period of geological time, to the strata of which has been 

 applied the name of " Laramie group," (Point of Rocks group of 

 Powell). His investigations also show that the strata, which in former 

 reports by himself and Professor Powell have been referred to the base 

 of the Wasatch group, also belong to the Laramie group, and not to 

 the Wasatch. He has reached this later conclusion not merely because 

 there is a similarity of type in the fossils obtained from the various strat 

 of the Laramie group with those that were before in question, but by 

 the specific identity of many fossils that range from the base of the 

 Laramie group up into and through the strata that were formerly re- 

 ferred to the base of the Wasatch. Furthermore, some of these species 

 are found in the Laramie strata on both sides of the Rocky Mountains. 

 Thus the vertical range of some of these species is no less than three 

 thousand feet, and their present known geographical range more than a 

 thousand miles. 



Besides the recognition of the unity of the widely-distributed mem- 

 bers of the formation of this great geological period, bounded by those 

 of undoubted Cretaceous age below and those of equally undoubted 

 Tertiary age above, his further observations have left comparatively 

 a s ii 



