GEOLOGICAL SUEVEY OF THE TERRITOEIES. 121 



mountains only from Cheyenne southward, it is very doubtful whether 

 the five distinct groups of strata would have been made out. The three 

 divisions, upper, middle, and lower cretaceous, are more natural south 

 of the North Platte, inasmuch as l!fos. 2, 3, 4, and 5 pass into each other 

 by imperceptible gradations. Though very few organic remains are ob- 

 served in them, yet I have never found the slightest difficulty in detect- 

 ing the different divisions at a glance by their lithological characters, 

 but I find it quite impossible to draw any line of separation that will be 

 permanent. Quite marked changes occur in the sediments of these 

 divisions in different parts of the West, but by following them continu- 

 ously, in every direction, from their typical appearance on the Upper 

 Miss€uii, the changes are so gradual that 1 have never lost sight of 

 them for a mile, unless concealed by more recent deposits. 



As I have before stated, I regard the group of sandstones which are 

 always found between well-defined cretaceous No. 2 and the Jurassic 

 beds as No. 1, or transition. No. 2 is certainly well shown, with many of 

 its features, but it is a black shale, often arenaceous, containing many lay- 

 ers of sandstone with some concretions; but so gradually passing up into 

 No. 3 that it is quite impossible to separate the two. Only in thin portions 

 of either Nos. 2 or 3 do we find any resemblance to the same groups as 

 shown on the Upper Missouri. No. 3 is a thinly-laminated yellow 

 chalky shale with some layers of gray, rather chalky limestone, always 

 containing an abundance of Inoceramus, doubtless I. problematicus, and 

 Ostrea eongesta. Eemains of fishes are almost always found in the dark 

 shales of No. 2. The black shales of No. 4 are quite conspicuous and 

 well marked, and have been quite thoroughly prospected for coal, but 

 to no purpose. These black shales pass gradually n]) into yellow rusty 

 arenaceous clays which characterize No. 5 ; and No. 5 passes up into the 

 lignite tertiary beds, where they can be seeii in contact, without any 

 well-defined line of separation that I could ever discover. But few 

 species of fossils are found in Nos. 4 and 5 in their southern extension, 

 but Baculites ovatus and several species of Inoceramus Ammonites, &c., 

 are common. Another feature is well marked here, and that is, there 

 are no beds that indicate long periods of quiet deposition of the sedi- 

 ments. Nearly all the sediments indicate either comparatively shallow 

 water or currents more or less rapid. 



Sometimes a single ridge will include all the beds of one formation, 

 or even those of two or three. I have often seen the sandstones of No. 1. 

 the Jurassic, and a portion of the triassic included in one ridge and the 

 adjoining valley. Again, a single formation will be Si)lit up into two or 

 more ridges. 



On the Cache a la Poudre, about a mile above Laporte, on the south 

 side of the river, the sandstones of No. 1 are separated into four success- 

 ive ridges, inclining, respectively, 18°, 21°, 35°, and 46° about southeast. 

 Much of this sandstone is a fine-grained grayish white, and rusty yellow 

 color, sometimes concretionary, or like indurated mud. Here all the divi- 

 sions of the cretaceous extend eastward in low ridges until they die out 

 in the plains or are concealed by the overlying tertiary. Along the Cache a 

 la Poudre and its branches is a series of terraces which are quite uniform. 



This valley is one of the most fertile in Colorado. The present year 

 there has been so much rain that irrigation has been unnecessary. The 

 bottom lands are about two miles wide, and thickly settled from mouth 

 to source. The grass is unusually fine this year everywhere. 



July 2. — In company with Dr. Smith, of Laporte, I visited the sup- 

 posed gold and copper mines at or near the sources of the Cache a la 

 Poudre Eiver. This stream makes its way through what might be called 



