110 REPOET UNITED STATES GEOLOGICAL SURVEY. 



edge we have of any given subject at a given time. In case, therefore, 

 if we have come to definite conclasious regarding the existing or want- 

 ing affinities of a particular group, we can most readily express our con- 

 victions by applying to the group the conventional systematic term 

 equivalent thereto. Such I deemed necessary in this instance. Instead 

 of regarding tbe " Laramie Beds " as simply a group of one or the other 

 formation, I treat it as an independent formation. It possesses its own 

 l)eculiar characteristics, it brings to its highest development and essen- 

 tially closes a chapter in the book of geological history. 



Within my districts the hirgest development of the Laramie forma- 

 tion is found in the Raton Hills.* Near Caiion City another outcrop 

 of it occurs, and again I found it on the west slopfe of the Great Hogback 

 in the White River district. The exposures in Southern Colorado show a 

 far greater vertical as well as horizontal development. There the forma- 

 tion reaches a thickness of about 2,700 feet, and expands over a large 

 area of country. Special features hav^e been described in the various 

 reports. The coal obtained from banks belonging to the Laramie is the 

 "lignite" of the West. In the strict acceptation it is not a lignite, but 

 a bituminous coal, some of which is coking, while other portions or veins 

 are non-coking. For ordinary economic purposes the coal answers very 

 well, and its present employment in this way is satisfactory. Enormous 

 quantities of it are bidden away awaiting but the active hand of the 

 miner, which shall bring it forth and rend^ it subservient to the uses 

 of man. 



TERTIARY. 



In the districts I have examined in Colorado I have observed two 

 groups of the Tertiary lormation. Local deposits of small extent belong- 

 ing to the Miocene period occur at a few isolated localities. They are in 

 no direct connection with the widely-extended areas elsewhere. At the 

 same time, it becomes a matter of some difficulty to identify them with any 

 particular portion of the synchronous groups. This characteristic will be 

 found to hold good for a large number of the Western Tertiary localized 

 groups. W^henever or wherever the connection between such groups and 

 the extended series of contemporaneous formations can be established 

 they fall into their places very naturally. It is necessary, therefore, to 

 examine, first of all, the correlations of isolated groups, and not at once 

 distinguish them by specific names that only add to subsequent confu- 

 sion in classification. Those small groups mentioned above as existing 

 in Colorado are altogether too unimportant to be distinguisued in any 

 marked manner. The largely extended series of Tertiary beds are suffi- 

 ciently characteristic in Colorado to admit of regularly taking their 

 systematic position. 



Wahsatch Group (Eocene). — The largest development of this group 

 occurs in Southern Colorado. In the district of 1875 the Laramie 

 formation is wanting near the Animas drainage, and we here find that 

 the Wahsatch beds rest directly upon the Fox Hills Group. Tlieir lowest 

 strata compose that series which Cope has named the Puerco marls. 

 Above that the alternating beds of sandstone and shale set in. Again, 

 we find Wahsatch in the W^hite River district. It there overlies the 

 Laramie, and is succeeded by the Green River Group. Wherever ero- 

 sion has carried away the superincumbent beds of younger age, there 

 the Wahsatch protrudes. A remarkable regularity of stratigraphical 

 condition characterizes the beds belonging to this group wherever I 

 have observed it in Colorado. Coal occurs in several members of the 



"'^ * Compare Rep. U. S. Geo. Survey, 1875, pg. 192. 



