630 EEPORT UNITED STATES GEOLOGICAL SUEVEY. 



members of the survey. The group of strata referred to the formation 

 is the Laramie Group, in regard to tJie age of which so much has been 

 written. The transitional character of the beds was long ago noted by 

 Dr. Hayden and other "writers. As long as the evidence presented by 

 the various organic contents is conflicting, it seems best to retain the 

 term Post-Cretaceous. 



The areas from w^hich fossils characteristic of the group were obtained 

 in our district may now be briefly enumerated. 



Green River Basin. — Along the eastern foot of tlie Wyoming Eange, 

 between it and meridian fold, that marks the rim of the Green Eiver 

 Basin, there is a series of greenish-gray sandstones with shaly bands, 

 which rest on the beds that I have referred to the Cretaceous. The ends 

 of these sandstones, dipping westward, abut against the westward- 

 dipping limestones of the range. The line of junction marks the line of 

 an immense fault. This fault is some 2,000 or 3,000 feet, the downthrow 

 being on the east. A similar fault is seen along the east side of the Salt 

 Eiver Eange, but whether or not there are any Laramie beds involved 

 here I cannot say at present. 



The line of junction between the Laramie beds and the Carboniferous 

 limestones is generally obscured by debris. I was not 'able to get a good 

 section, but there must be in the neighborhood of 4,000 feet of sand- 

 stones referable to the group along the foot of the range. It is probable, 

 also, that the entire thickness of the group is not exposed. Following 

 the folding and faulting which affected these beds, there was a period 

 of erosion x:)receding the deposition of the Wahsatch Group. The latter 

 is unconformable to the Laramie Groui3 along the entire range, while 

 the Laramie api)ears to be conformable to the underlying formations. 

 At the bend of Ham's Fork there is an outcrop of sandstones, from which 

 Laramie fossils were obtained, but there is a fault at this locality which 

 has confused the relations of the strata, and it is not certain that the 

 fossils obtained were in place. 



The line of the faidt along the eastern side of the Wyoming Eange is 

 not a straight line ; but the Laramie sandstones fill bay-like recesses in 

 the Carboniferous limestones of the range. This is especially the case 

 in the northern portions, and led me at first to think that the range had 

 formed a portion of the shore of the Laramie Sea ; but afterwards the 

 contact of the sandstones with the limestones was well seen, and the 

 former were seen to have a dip to the westward against the limestones, 

 which also dip to the westward. It was clearly seen to be a lault. The 

 latter seems to have taken place a little after the sandstones were folded, 

 or perhaps they were crowded against the mass of Carboniferous lime- 

 stones at the time the fault occurred. The conditions here are shown 

 in the sections of Meridian fold in Chapter III. 



Tliere was no evidence in the Laramie beds of the immediate proxim- 

 ity of the shore during their deiDOsition, as there was in the beds of the 

 Wahsatch Group. 



SmitJi's Fork and Bear River region. — Along the east side of Bear 

 Eiver, between the valley and the mountains, is a comparatively low 

 area of sandstones, which sometimes assume the character of low hog- 

 back ridges. These sandstones are gray and greenish gray. They are 

 folded corresponding to the folds of the older rocks. On Twin Creek 

 they are seen below Wahsatch conglomerates, which rest on their uj)- 

 tiu-ned edges. Here there are layers of coal, from which unmistakable 

 Laramie fossils were obtained. On Smith's Fork, also, a bed of coal out- 

 crops, and from it a few forms were obtained. 



Korth of this region, near Station 41, another fossil locality was noted. 



