32 GEOLOGICAL SURVEY OF THE TERRITORIES. 



the vast erosion that must have taken place here, to have removed so 

 great a thickness of strata from so vast an area. 



The bluffs east of Colorado Springs, above that portion shown in Sec- 

 tions a and b, may be regarded as barren of workable beds of coal. A 

 detailed section of the beds was taken, but it seems hardly necessary 

 to present it here. So variable are these beds that the sections within 

 a fourth of a mile would only bear a general resemblance to each other. 



The beds are made up of alternate layers of clay and sand, with irregu- 

 lar beds of concretionary sandstone throughout. These beds of sand- 

 stone change constantly, sometimes 30 feet in thickness, and quite mas- 

 sive at one point, and within a fourth of a mile either thinning out or 

 changed into soft or indurated sand. Toward the. summit of the bluffs 

 is a thick bed of rusty-brown sandstone, which has been worn by the 

 atmosphere iuto remarkably rugged forms. As we proceed northward 

 from Colorado Springs to the source of Monument Creek, on the divide 

 between the South Platte and the Arkansas drainage, the upper beds 

 of the Lignitic group appear entirely destitute of coal, with a vast thick- 

 ness, estimated at 1,500 to 2,000 feet, with unusually coarse sediments. 

 The materials composing these Upper Lignitic strata of the Monument 

 Creek present the appearance of having been deposited with unusual 

 rapidity in moving or disturbed waters. Figures show with great 

 clearness this peculiar character of the sediments. The peculiar group 

 of strata which, in 1869, I called the Monument Creek group, extends to 

 a point within about twenty miles of Denver, where the Lignitic sedi- 

 ments return to their usual character, and then continue northward 

 nearly to Cheyenne. 



For a distance of about thirty miles north of west of Monument Creek, 

 the coarse variegated sandstones of the Monument Creek group lap on 

 to the granites, have been slightly elevated so as to incline 5° to 15°, 

 but not detached from the granites, so that for a considerable distance 

 these granite foot hills formed the western shore-line for the great lake. 

 This group is more fully treated in a subsequent portion of this chap- 

 ter. 



Up to the present time, but few invertebrate remains have been found 

 in the Lignitic group from the Arkansas to Denver; but in the lower 

 strata in the vicinity of the coal-beds a number of plants have beeii 

 observed, belonging in most instances to well-known species occurring 

 elsewhere. These plants were observed by the Survey in several locali- 

 ties along the southern border of the group, generally in the bed of sand- 

 stone immediately below the lowest coal, and ranging up 100 to 150 feet. 

 The species, as identified by Lesquereux, are Sabal Campbelli, Piatanus 

 Haydeni, Ficus UllcefoUa, Dombeyopsis obtusa. The Sabal has been 

 found at Eaton Hills, Golden City, Black Buttes, and on the Upper 

 Missouri Biver near Fort Union. The Piatanus occurs at Baton 

 Hills, Golden City, Black Buttes, and was originally described from the 

 Upper Missouri Biver, where it is found in great numbers. The Ficus 

 has been obtained from Evanston on the Union Pacific Bailroad, Baton 

 Hills, and in Montana on the Yellowstone, so that the evidence, so far 

 as it can be derived from the few vegetable remains, connects this group 

 with the Baton Hills group to the southward, and far to the north on 

 the Upper Missouri. Other species have been identified. 



From Colorado Springs, we may follow the Lignitic group northward 

 very nearly to Cheyenne without any break. For a short distance, as 

 we have previously remarked, the Monument Creek group laps on to the 

 granites, entirely concealing all older formations; but very soon after 

 crossing the "divide" to the drainage of Plum Creek, the older beds re- 



