44 GEOLOGICAL SURVEY OF THE TERRITORIES. 



the graDitic range. In the annual report for 1873 the fact was stated 

 that the Eed Beds, in the form of coarse conglomerates, filled up the 

 uneven surface of the granitic rocks below. South of Manitou we 

 find an enormous thickness of very coarse conglomerates, cemented with 

 rather fine sands, jutting up against the mountain-sides, showing clearly 

 that, although elevated and disturbed to a certain extent since their 

 deposition, they were laid down along the base of the Front Eange as a 

 shore-line, and that there must have been a period of comparative re- 

 pose. When these sandstones, near the base of the mountains, are ^oiind 

 to be made up of conglomerates, they are observed to be very coarse 

 in the immediate vicinity of the granites, but becoming finer and finer 

 sandstones as they extend eastward into the plains. There should there- 

 fore be some nonconformity between the Triassic and the Carboniferous 

 and Silurian groups below, for both of the latter extend high up on the 

 flanks of the mountains on either side, sometimes occurring on the sum- 

 mits of the lower ranges. The section in Plate VII would indicate some- 

 thing of this sort, for we find the Silurian and Carboniferous inclining 

 20° and 45°, while the Triassic dips 90°, or is very near a vertical. The 

 diagram also shows how the Silurian beds lie high up on the granite 

 flanks of the mountains. The elevatory force seems to have acted ver- 

 tically, bending the overlying sedimentary strata like metallic sheets, so 

 that within a few yards of the nearly vertical beds the same are hori- 

 zontal or nearly so. This will explain very clearly the abruptness with 

 which the mountains seem to rise out of the plains to the traveler ap- 

 proaching them from the east. 



The beautiful pictorial section of Pleasant Park may need a word of 

 explanation here. The dotted line a a shows that all the felevated por- 

 tion in the rear or west of it is composed of granitic rocks. The dotted 

 line in the foreground, li h, shows the junction of the Lignitic group 

 to the true Cretaceous beds which here rise up in a very narrow belt 

 from beneath the Monument Creek group. It is exposed by the wear- 

 ing away of the Monument Creek beds. The letter i indicates the 

 usual form and isolated character of the numerous buttes that are scat- 

 tered over the plains here for a considerable distance east of the mount- 

 ains. The strata are nearly horizontal, the summits are flat, table- 

 shaped, and are not unfrequently capped with trachyte. Between the 

 dotted lines the Carboniferous, Eed Beds (Triassic), Jurassic, and Cre- 

 taceous groups are exposed. The manner of inclination and the rela- 

 tion of these groups to the granitic range, as well as to each other, is 

 made clear by the section. 



THE JURASSIC. 



This formation has already been described in so much detail in pre- 

 vious reports, that I shall mention it very briefly in this connection. 

 Far to the north this group holds a prominent position, not only on ac- 

 count of its aggregate thickness, but also from the abundance and 

 variety of its organic remains. South of the Union Pacific Eailroad, in 

 Colorado, it is confined to a very narrow belt, with very few if any fos- 

 sils to establish its age. That it extends most persistently far south- 

 ward into New Mexico, there cannot be a doubt. The narrow belt which 

 it occupies is well shown in the small map of Colorado Springs and vi- 

 cinity. North of the Pacific Eailroad, along the base of the front range 

 of mountains, it increases in thickness and is full of characteristic fos^ 

 sils. In the annual report for 1873 and previous reports, the lithologi- 

 cal characters of all of these groups have been so fully discussed that it 



