30 GEOLOGICAL SURVEY OF THE TERRITORIES. 



The inclination is slight, 5° to 10°, about ; northeast. The bluff- wall 

 undoubtedly extended at one time over the entire interval south and 

 southwest and was joined to the Cafion City group ; the intervening por- 

 tions having been removed by erosion, with the exception of a narrow 

 belt just at the base of the mountains. This interval is entirely occu- 

 pied with Cretaceous rocks at the present time. The valley of the 

 Fountain, as well as that of Monument Creek, for some distance above 

 its junction with the '^Fountain, is underlaid with Upper Cretaceous 

 groups Nos. 4 and 5 ; but the surface is everywhere so denuded and 

 grassed over that the junction of the Cretaceous with the Lignitic group 

 is nowhere well marked. 



The lower bed of sandstone, which is usually regarded as the com- 

 mencement of the Lignitic, iscomposed sometimes of yielding arenaceous 

 sediments, and therefore cannot always be relied upon as forming a fixed 

 horizon of demarkation. But, in the majority of instances, this floor of 

 sandstone is present with a greater or less thickness. About ten miles 

 east of Colorado Springs, some very important coal-beds have been 

 opened by Mr. Matt France and others. This locality is a very import- 

 ant one for the study of this great coal-group. Between Colorado Springs 

 and the coal-mines, the intervening country is very rolling or undulating, 

 and so grassed over that no sections of the underlying beds are exposed ; 

 but, before reaching the mines, the rounded grassy hills are covered with 

 fragments of calcareous concretions, from which have been taken a great 

 variety of the fossils characteristic of the Upper Cretaceous. The three 

 forms which are usually so abundant, Ammonites lobatus, Baculites ova- 

 tus, and Inoceramus, are here found in great numbers. This point is about 

 600 feet higher than Colorado Springs; and inasmuch as the strata are 

 horizontal, we may estimate the thickness of the Cretaceous beds above 

 the valley of Monument Creek at GOO to 800 feet. As we continue to 

 the west we soon come to dark, rusty-brown sandstones, with great 

 numbers of a peculiar kind of sea-weed, called by Mr. Lesquereux Haly- 

 menites. There is a series of alternate layers of arenaceous clay and 

 sandstones, 200 feet or more in thickness, the upper portion containing 

 vast globular concretions, as illustrated in Plate 4, Fig. 2, which corre- 

 spond to the mud-beds seen in the vicinity of the coal-basin of the 

 Arkansas. A section of the beds here would be as follows, in ascending 

 order : — 



Section a. 



Ft. 111. 



1. Coal 8 



2. Clay 6 



3. Sandstone 7 



4. Clay 16 2 



5. Yellow sandstone 5 



6. Solidcoal 8 1 



7. Rusty-brown clay and sandstone 50 — 80 



8. Alternate layers of sandstone and clay 200 



9. Cretaceous formations Nos. 4 and 5 600 — 800 



This section is in part constructed from shafts that have been sunk 

 for coal. So far as I have observed, the only way to obtain a clear sec- 

 tion of the coal-strata, is by boring or sinking a shaft. All other sec- 

 tions, unless made in some actual cut, may be regarded as only ap- 

 proximately correct. The lower portion of section a, Cretaceous, grad- 

 ually passes up into bed 8, which is composed at the bottom of alter- 

 nate thin layers of sandstone and clay, these layers increasing in 

 tliickness toward the top. The upper portion is made up mostly 

 of rounded concretions, varying in size from an inch or two to sev- 



