124 GEOLOGICAL SURVEY OF THE TERRITOEIES. 



more conspicuous at all times along- the foot-liills of the mountains, even 

 to New Mexico, than any other portion of the cretaceous sfroup. 



The valley of Thompson Creek is very fertile, varying from half a 

 mile to a mile in width, is filled up with settlers, and most of the land 

 is under a high state of cultivation. The creek itself is one of the pure 

 swift-flowiDg mountain streams which have their source in the very 

 divide or summit of the water- shed, and are rendered permanent by the 

 melting of the snows. All these mountain streams would furnish abund- 

 ant water-x)ower, most of them having a fall of thirty feet to the mile. 



There seems to be a decided improvement in the soil as we go south- 

 ward. The geological formations are the same, but the climate is more 

 favorable. 



On a terrace on the north side of Big Thompson Creek there is a bed 

 of recent conglomerate, quite perfect, and belonging to the modern drift 

 period. It is very coarse, and the worn boulders are held together by 

 sesquioxide of iron. I note it here as an example of very recent conglom- 

 erate. There is much fine sand, and the rounded stones are exactly 

 like those which pave the bottoms of streams. The thickness of this 

 boulder deposit is considerable, and it seems to underlie the whole val- 

 ley portion of the country. 



The cretaceous beds of No. 3 pass down into a yellowish sandstone 

 which forms a low ridge on the north side of Big Thompson Creek. 

 Two or three low ridges of cretaceous appear east of this jDoint, but die 

 out in the prairie. This ridge inclines 15°, then comes a valley about 

 one-fourth of a mile wide, and a second ridge of rusty reddish fine- 

 grained sandstone, evidently No. 1, or the transition group. This ridge 

 inclines 25°. Underlying the sandstone, which forms a large part of 

 this ridge, we find the ashen-gray marly and arenaceous clays of the 

 Jurassic, including some thin beds of sandstone and one layer of lime- 

 stone four to six feet thick, which has been much used for lime among 

 the farmers. These beds pass down without any perceptible break into 

 the light brick-red sandstones which form the next two ridges west- 

 ward. These beds have a dip of 30°. About the middle of the red 

 beds there is a layer of impure limestone standing nearly vertical Go^, 

 two to four feet thick, which has also been used somewhat for lime. 

 The next ridge west has a rather thick bed — ten to fifteen feet — of very 

 rough impure limestone looking somewhat like very hard calcareous 

 tufa. The intermediate beds are loose brick-red sands. 



There is here a somewhat singular dynamic feature — a local anticli- 

 nal. One of the ridges flexes around from an east dip to a west dip, from 

 the fact that one of the eastern ranges of mountains runs out in the 

 prairie near this point, forming at the south end originally a sort of 

 semi-quaquaversal, the erosive action having worn away the central 

 portions. This forms a short anticlinal of about a mile in length. On 

 the east side of the anticlinal valley the principal ridges are shown, inclu- 

 ding nearly all the red beds ; and on the west side, only the upper portions 

 of the red sandstones with the Jurassic beds and the transition sand- 

 stones. The latter rocks form the nearly vertical wall in which is 

 located a somewhat noted aperture called the "Bear's Church." In the 

 west part of this anticlinal, within twenty feet of the brick-red sand- 

 stones, is a blue, brittle limestone layer about six feet thick, inclining 

 seventy-eight degrees. This west portion of the anticlinal might be 

 described across the upturned edges thus, commencing at the bottom : 



1. Rather I'ght brick-red sandstones in three layers — estimated 200 

 feet. 



