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w 
and especially in the west; that from Northern New Mexi¬ 
co to Southwest Wyoming the various members of the Cre¬ 
taceous lie in almost unbroken belts. 
TT Between the east and the west there is only 
one incongruity. Along the east base of the mountains 
the Upper Cretaceous rocks, including Nos. 4 and 5, are 
almost wanting, consisting at most of a few hundred 
feet of shales and laminated sandstones. Along the west 
base this group becomes a prominent and important topo¬ 
graphical as well as geological feature. In the South¬ 
west, where it forms the "Mesa Verde" and the cap of 
the Dolores Plateau, it comprises upward of two thou¬ 
sand feet of coal-bearing strata, chiefly sandstone, 
while in the north it reaches a thickness of 3,500 feet, 
and forms the gigantic "hog-back" of the Crand River 
Valley. 
"While in the southwest he visited the Sierra 
Aba jo, a small group of mountains, which lie in Eastern 
Utah, and found, as he had previously surmised, that 
the structure was identical with that of the four other 
isolated groups that lie in the same region. A mass 
of trachyte has been forced up through fissures in the 
sedimentary rocks, and now rests chiefly upon the sand¬ 
stones and shales of the Lower Cretaceous. There is a 
considerable amount of arching of the sedimentary rocks, 
caused probably by the intrusion of wedge-like sheets of 
