136 ENVIRONMENT OF VERTEBRATE LIFE, ETC. 



The upper layers are compact, hard, pink, and cream-colored quartzites, with 

 occasional intercalated beds of limestone. The base consists of 80 feet of impure 

 limestones with interbedded red magnesian shales that are soft and weather 

 readily, their red muds staining the harder rocks. 



"In going northward the formation changes greatly in character and thick- 

 ness. In the Little Belt Range the quartzites disappear and the most character- 

 istic feature is the presence of a shale horizon— the Otter shale— whose vivid green 

 color makes it conspicuous wherever exposed. At the same time the formation 

 becomes of a variable nature. Limestones, sandstones, and shale beds appear, but 

 are not persistent. On the Judith River the base of the formation consists of the 

 red Kibbey sandstone, which frequently contains beds of gypsum. The thickness 

 of the formation is nearly 1,400 feet at this locality, while it is but 400 feet north 

 of Castle Mountain. The limestones carry abundant fossil remains, fixing the age 

 as lower Carboniferous. * * * The region was probably elevated above the sea 

 at the close of the Quadrant stage." 



In the Fort Benton quadrangle, the quartzite has almost entirely given 

 place to shales and limestones. Weed says of the horizon:^ 



"Within the limits of this quadrangle the Quadrant formation is a variable 

 sequence of sandstones, shales, and limestones. The lowest beds are reddish 

 and yellow clayey sandstones, often holding interbedded layers of gypsum and 

 constituting the Kibbey sandstone. These are overlain by the Otter shales 

 holding interbedded limestones. The shales are dark gray or purplish near the 

 base, becoming a bright coppery-green higher in the sequence. The interbedded 

 limestones are very seldom more than a foot or two thick, are frequently oolitic, 

 and carry fossils of lower Carboniferous types. 



"[The Quadrant formation] shows a very decided change of conditions of 

 deposition, indicating a rising of the region, with shore and estuarine deposits 

 which preceded the emergence of this tract above the sea. The change from pure 

 limestone to red sandstones with gypsum beds and limey shales is abrupt, but 

 the Quadrant contains also several beds of very pure limestone. 



"* * * though there is a marked change in the character of the forms of life, 

 there is little change in the character of the beds between this and that of the 

 overlying Ellis formation, whose fossils are of the Jurassic age." 



Beyond Philipsburg and Fort Benton, Montana, there are no reported 

 exposures of any formations that can be at all closely correlated with the 

 Weber horizon, but as it has been shown that in this region the Weber is 

 becoming more of an offshore formation with increasing limestone and is 

 the uppermost Paleozoic exposed, it is possible to at least trace the upper- 

 most Paleozoic farther to the north and west. The condition along the 

 boundary between the United States and Canada is condensed from Daly 

 on pages 1 71-178, and this area of limestone and quartzite of upper Penn- 

 sylvanian age is with little doubt to be correlated in a broad way with the 

 Cache Creek series of British Columbia and as far north as the Yukon 

 Territory and with the similar deposits of Alaska. 



(i) Conditions on the Pacific Coast.— On the west side of the western cor- 



1 Weed, W. H., Fort Benton Folio, No. 55, U. S. Geological Survey, p. 2, 1899. 



