PEALE.] 



GEOLOGY SECTION NO. 2, 199 



near Colorado City, it probably continues southward uninterruptedly. 

 It can be traced northward as far as Spring Creek, but above that 

 point seems to be covered. Whether or not it is present at the 

 the Platte Kiver I could not determine, as the space where it wouM be 

 found was covered so that all the beds were totally concealed. The 

 space (So. 21) below the gypsum is probably filled with shales and iime- 

 stoues. That above is filled with the shales just below Ko. 1 Cretaceous, 

 which is represented in No. 20. The general color of these sandstones 

 is a yellowish white, becoming pink below. No. 27 is filled, in all i>rob- 

 ability, by the sandy shales of Cretaceous No. 3. Everything is con- 

 cealed until we reach 28, where we find the same fossiliferous limestone 

 that we have in bed 2 of the Platte section, and outside of it the out- 

 crop of the white, chalky-looking limestone with cross fracture. From 

 this outcrop, which forms a low ridge outside of the hog-backs, we have 

 no exposures until after we have crossed West Plum Creek, a distance 

 of about three-quarters of a mile. This would give us, with the dip at 

 10°, a thickness of about 700 feet of strata, mostly the shales of No. 

 4 and the upper part of No. 3, to which No. 28 of the section is referred 

 and of which it forms the lower part. Beds 30 to 38, inclusive, I have 

 referred to No. 5 Cretaceous, although I could find no fossils to prove 

 the correctness of the opinion. Their position and lithological charac- 

 ter warrant their being so considered. The dip of these beds is about 

 20°. The junction between them and the horizontal sandstones in the 

 butte shown in the section could not be seen, as the base of the butte 

 is covered with debris. At the base of the butte is a thickness of 

 about 840 feet of rather coarse sandstones. Some of the layers are rusty- 

 colored, and they are nearly, if not quite, horizontal. They are capped 

 with a layer of light purplish trachyte. This capping is about 20 feet 

 in thickness. The area of this mesa or table-like butte is about 30 

 acres. As we approach the Colorado divide, the Tertiary sandstones 

 reach to the mountains, resting on the upturned edges of the older 

 formations. Plum Creek and its branches have cut their valleys 

 through these sandstones and conglomerates. Throughout the valley 

 of Plum Creek we find numerous mesas, and all that I Visited were 

 capped with trachyte. The origin of this volcanic material I was 

 unable to determine. These sandstones probably belong to the Mon- 

 ument Creek group, and once extended to the edge of the mount- 

 ains along the whole range as we still see them on the divide. The 

 summits ot the mesas show us the original surface before the eroding 

 agents had commenced their work. The Colorado divide, or Pinery, is a 

 ridge with a mesa-like top extending eastward from the mountains. It 

 is merely the undisturbed sandstones of the Monument Creek group, 

 capped with the trachyte layer, and forms the water-divide between the 

 branches of Monument Creek, which flow southward to the Arkansas 

 Ptiver, and the waters of Plum Creek, which empty to the northward in 

 the South Platte Eiver. The divide is well timbered, and is already the 

 seat of an extensive lumber trade. The shrill whistle of the steam saw- 

 mill echoes and re-echoes among the hills, while the valleys are all being 

 rapidly settled and the capabilities of the land for agricultural pursuits 

 being demonstrated. On the divide close to the mountains, the eroding 

 forces have cut a narrow pass in the Monument Creek group, and the 

 fragments of these sandstones are seen resting immediately on the 

 granites, while to the eastward the beds continue uninterruptedl3^ 



This pass is about half a mile in width, and through it the Denver and 

 Eio Grande Pailroad crosses on its way southward. In the sandy debris 



