166 GEOLOGICAL SURVEY OF THE TERRITORIES. 



some finer uiicompacted sediments. Farther out they are of soft, 

 crumbling, white marls, with surfaces usually sprinkled with bould- 

 ers, often quite large pieces of metamorphic rocks, as remnants of a 

 bed which had existed above the present surfaces, and had been eroded 

 away. It was in this neighborhood that the following section. Fig. 12, 

 was observed and illustrated by Mr. Holmes, when accompanying Dr. 

 Hayden's party, and shows well the characteristic weathering of these 

 soft beds when exposed, as sometimes happens, in a cliff. Here also is 

 an inclination in these recent beds of 10° to the east. Thus, a greater 

 part of the eastern corner of the map is of lake-beds, in i)art covered 

 with basaltic lava, and at the east abutting against an outcropping fold 

 and ridge of Cretaceous sandstones, which dip west beneath them, and 

 rest on metamorphic rocks. They form a flat terraced and treeless val- 

 ley, but at the north and west rise in higher bulky hills. Just west of 

 the junction of the Frazier with the Grand rises an abrupt, sharp, well- 

 defined ridge, several hundred feet high, which is broken through by the 

 river in a narrow gate-way. Just outside of this gate- way, at the north 

 side of the stream, and directly beneath the ridge, there are exposed by 

 the ravines cutting through the terraced lake-beds, a thickness of about 

 300 feet of brown concretionary, friable sandstones — the characteristic 

 features of Cretaceous No. 5 — and which yielded an Inoceramus and 

 joints of BacuUtes. These beds dip westward beneath the ridge at an 

 angle of 25^. The gate-way exposes the larger ridge to be composed of 

 a rough, sedimentary aggregate of volcanic material; a series of con- 

 glomerates, breccias, sands, and irregular material, of which the most 

 distinct rock is of a doleritic character, consisting of a gray granular 

 base, containing occasional small crystals of a trichinic feldspar, and 

 more numerous, larger, and well-defined crystals of augite. This more 

 compact portion is a similar rock to the lava dike resting in the siliceous 

 sandstones near the entrance of the park. 



This volcanic detrital series attains an estimated thickness of from 800 

 to 900 feet ; the lower i)art being a massive accumulation, and not show- 

 ing distinct stratification, the upper part being well bedded, and often of 

 fine materials. These strike nearly north and south, and dip westward 

 at an angle of 60°, though the higher portion of the ridge on the south 

 shows an abrupt bend, dipping but 25° or 30° west, (see section.) 



Passing down- stream through this gate- way, the valley again opens 

 out, but its character changes entirely. The beds that lie above the 

 doleritic breccia and sands, though likewise abruptly turned up and 

 dipping west immediately adjacent to them, suddenly become nearly 

 horizontal, with a gentle northern dip, and form, all along the north 

 side of the Grand, a series of regular and high terraces running in long 

 tongues out toward the river. 



There are two principal terraces, the lower one rising nearly a 

 thousand feet, and attaining this level between one and two miles back 

 from the river. Harder beds on its face break up the front slope of this 

 terrace, tending to mold its face into minor terraces two or three 

 hundred feet high. 



The second terrace stands about a half mile back from the edge of 

 the lower one, and rises in a more even slope, unbroken by intermediate 

 beds, to an altitude of about a thousand feet above it. The accom- 

 panying section, Fig. 13, gives an idea of the profile of these well-marked 

 terraces, which attract attention even from Long's Peak far to the east. 



Back a few miles rises still another terrace, estimated at about half 

 the height of the last one, or about 500 feet. Estimating that there 

 were at this point about 100 feet of beds beneath the river, and be- 



