HGiioss ran the haydue survey. ie?6 
"In company with the triangulation party, Mr. 
Holmes made a hurried trip through Colorado, touching also 
portions of Hew Mexico and Utah. Ee was unable to pay much 
attention to detailed work, but had an excellent opportunity 
of taking a general view of the two great plain belts that 
lie, the one along the east, the other along the west base 
of the Rocky Mountains. For nearly two thousand miles travel 
he had constantly in view the Cretaceous and Tertiary forma¬ 
tions, among which are involved some of the most interesting 
geological questions. He observed, among other things, the 
great persistency of the various groups of rocks throughout 
the east, west, and north, and especially in the west; that 
from Horthem. Hew Mexico to Southwest Wyoming the various 
members of the Cretaceous lie in almost unbroken belts. 
"Between the east and the west there is only one 
great incongruity. Along the east base of the mountains the 
Upper Cretaceous rocks, including Eos. 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 topographical as well as 
geological feature. In the southwest, where it forms the 
"Mesa Verde” and the cap of the Dolores Plateau, it comprises 
upward of two thousand feet of coal-bearing strata, chiefly 
sandstone, while in the north it reaches a thickness of £,500 
feet, and forms the gigantic "hog-back" of the Grand River Talley. 
"While in the southwest he visited the Sierra Aba^o, 
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 sandstones 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 trachyte, while 
the broken edges of the beds are frequently, but abruptly, press¬ 
ed up, as if by the upward of lateral pressure of the rising 
mass* Ee was able to make many additional observations on the 
geology of the San Juan region, and secured much v luable 
material for the coloring of the final map. 
"He states that the northern limit of ancient cliff- 
builders in Colorado aid Eastern Utah is hardly above latitude 
£7° 45'." 
(Tenth Annual Report of the U. S. Geological and Geographical 
Survey of t le Territories, 1876, by F. 7. Hayden, page XV) 
