Mesozoic and Ccenozoic Geology and Palceontology. 197 



succession of sandstones is interstratifiecl with shale. Selenite is com- 

 mon in the shale. The higher members of the group are composed of 

 yellow and white sandstones, containing beds of coal, and dark and 

 often carbonaceous shales. Sandstones mediate the transition into the 

 lower Tertiary groups. The lower coal- horizon is the most productive. 

 The total thickness of this group west of Rawlings Springs, and from 

 there northward, is estimated at 1,600 feet. 



The decomposition of pyrite in dumps from coal banks, produces a 

 spontaneous combustion of the coal which changes the color of the 

 shales to a brilliant red. In the same manner probably the coal at 

 places in the bank has taken fire and burnt as long as the supply of 

 ox3^gen could sustain a flame. Through this process of metamor- 

 phosis by heat the overlying beds, containing more or less hj^drated 

 ferric oxide, were changed to a bright vermilion color. Sandstones 

 occur, the faces and edges of which have been literally glazed by the 

 long continued action of heat. Fragments are firmh' baked together, 

 and resemble cinders from a furnace. Purely argillaceous shales 

 and cla3's have been thoroughly fritted and altered into very hard, 

 compact porcelain jasper. Throughout the area covered by the Lar- 

 amie Group, and in some of the Wasatch beds red colored strata 

 occur which have been produced by these causes. 



Dr. A. C. Peale,* estimated the thickness of the Laramie Group on 

 Smith's Fork, and in the Bear River region, near the western shore 

 line of the Wahsatch lake, at 5,000 feet. 



Geo. M. Dawson, f explored the Cretaceous in British Columbia, on 

 the headwaters of the Skagit, west of the main axis of the range, 

 which forms the watershed, between that river and the Similkameen. 

 The trail traverses the area in a general northeast direction for nearly 

 thirteen miles. A section occurs on the trail immediately east of the 

 crossing of the north branch of the Skagit, representing a thickness of 

 4,429 feet. The rocks are much disturbed, are lying at all angles up 

 to vertical, and have suffered considerable hardening and alteration. 

 Thej^ consist, generally, of sandstones, conglomerates and argillites. 



Still further north-westward, from the vicinity of the mouth of Ander- 

 son river and Boston Bar, the}^ were found to extend, in a long, narrow 

 trough, uearl}' coinciding, in the main, with the Frazer river, with a 

 general bearing of about N. 70° W., to the vicinity of Lillooet and 

 Fountain, a distance of about 80 miles. The estimated thickness is 



- nth Ann. Rep. U. S. Geo. Sur. T6rr. 

 T Geo. Sur. of Ciiu. 



