98 GEOLOGICAL SUKVEY OF THE TERRITOKIES. 



soft, aud though often forming a number of minor ridges, the latter no- 

 where rise in prominently continuous hog-backs, while, on the contrary, 

 they may be quite eroded away into a broad valley, with the Archaean 

 rocks forming its western side, the beds yet to be described forming their 

 bounding hog-backs in the east. They often rise, however, for consid- 

 erable distances up long gentle slopes of the mountain rocks, which 

 places them in a favorable position to be eroded into the peculiar and 

 grotesque forms which characterize the Garden of the Gods, which, how- 

 ever, is in a very different geological horizon, though somewhat simi- 

 larly circumstanced. The curious groups of worn rocks aud monuments 

 thus formed sometimes have their tops worn off horizontally, as if by the 

 surface action of the old retiring sea, while the same sub-aqueous erosion 

 has in places smoothly leveled off considerable areas of the upturned rocks, 

 as is best shown a few miles north of the South Platte. (See Plate II, 

 section 17.) 



THE JUKASSIC. 



General cMracters. — The series of strata lying next above the red beds 

 form a group of rocks in which the. thin-bedded and shaly element de- 

 cidedly predominates. The outcropping edges of these beds have there- 

 fore generally been more eroded away than the harder beds above and 

 below, so that they generally appear in valleys j and being soil covered, 

 they are not usually well exposed. 



The arenaceous element still predominates, though argillaceous mate- 

 rial is often present to a very large extent, while beds of impure lime- 

 stone occur — one of which appears very persistent — and gypsum is 

 frequent in thin layers, and sometimes occurs in workable quantities 

 and of good quality. As before, red is the prevailing color, though 

 a series of marked variegated colors occur, and weathering frequently 

 produces an ashen-gray tint upon the surface. A brief detail-description 

 of sections taken at several points will best convey an idea of the litho- 

 logical characters of the series, proceeding in each case from above down- 

 ward. 



Section of Jurassic heds near the Bear''s Church, Big Thompson Greek. — 

 Br. F. V. Sayden, Third Annual Eeport, 1869, reprint, p. 125. 



No. 



Nature of strata. 



Thickness 

 in feet. 



Top. 



Loose drab-yellow sand, debris of underlying beds^ one limestone 2 

 feet thick. 



Limestone, quite pure, blue, semi-crystalline 



Variegated clays 



Ashen clay, with six-tenths feet of blue cherty limestone, clay part- 

 ings 



Blueish limestone.. 



Fine bluish-brown sandstone 



Massive reddish-gray, rather fine sandstone 



Base. 



200 



25 

 4 



2 

 20 



