GEOLOGICAL SURVEY OF THE TERRITORIES. 49 



the west bank of the valley of Black's Fork, and from the margin we 

 obtained a most instructive view of the third or central belt. The west 

 side of the valley of Black's Fork is very steep, rising from eight hun- 

 dred to one thousand feet above the channel. It is covered very thickly 

 with transported boulders, most of which are but little worn. Here 

 and there are quite broad terraces, produced by land-slides. On the 

 opposite side are the high ridges of limestone which have been furrowed 

 down the sides by atmospheric forces in a somewhat striking manner. 

 The color and general appearance of the mass across the valley led me 

 to believe that it was the result of an outburst of igneous rocks, but on 

 closer examination I found it was an extension westward of Photo- 

 graph Bidge from Smith's Fork, and was composed of limestones of 

 carboniferous age. About two miles further up the west side of Black's 

 Fork we came to an exposure of the red-beds or triassic, the first dis- 

 play of them I have been able to find in the mountains. They are 

 shown here from one hundred and fifty to two hundred feet in thickness, 

 passing into grey sandstones quartzites and indurated arenaceous 

 clays: then alternate thin beds of gray limestone and sandstone, and 

 finally into the massive limestone that forms one of the most conspic- 

 uous ridges. The inclination of the beds appeared to be 46° northwest, 

 with a trend northeast and southwest. The red-beds being composed of 

 yielding sands and clays, are here worn away so that a low, narrow pass 

 was formed across the ridge between the west branch of Black's Fork 

 and the east branch of Bear River, revealing the beds of sandstone and 

 gray quartzites, the vertical layers projecting above the general level like 

 walls, and their height depended upon the power of the rock to resist the 

 atmosphere. Further up toward the sources of these rivers, where the 

 strata are finely exposed, we could see clearly that the limestones formed 

 a ridge of upheaval parallel with the axis of the mountains, and extend 

 off far to the southwest across all the branches of Bear River toward, 

 the Wasatch range. 



Among the numerous fossils that occur here in the limestones are 

 ZapJirentis, Productus Prattenianus, &c. Some of the layers of an 

 ashen-grey, compact limestone were mostly composed of fragments of 

 remains. The fossils, therefore, fix the age of the limestones that con- 

 stitute this ridge there, beyond a doubt. The same limestones undoubtedly 

 extend all over the Utah basin, along the western side of the Uintas, 

 along the flanks of the Wasatch range and about Salt Lake. Many of 

 the fossils appear to be identical with those from Salt Lake, described 

 by Hall in Stansbury's Report. The succeeding series of rocks I have 

 not found it so easy to locate in the geological scale. They consist of 

 dull, purplish sandstones, with a series of thin layers of slate and clay, 

 gradually passing down into quartzites. The upper beds are nearly 

 all sandstones of various degrees of texture ; some very fine and com- 

 pact, others an aggregation of small worn particles of quartz ; then a 

 complete pudding-stone, consisting of water- worn quartz j>ebbles set in 

 a silicious paste. As we proceeded toward the crest of the mountains, 

 the sandstones are very clearly shown in the sides of the valleys of both 

 Black's Fork and Bear River. As these diminish in importance, the 

 quartzites increase until the beds of reddish and gray quartzites are very 

 thick and massive, while the sandstones and slaty clays are thin and 

 unimportant, until we arrive at the main divide, where the rocks are 

 reddish quartzites alone. Between the east branch of Black's Fork and 

 the east branch of Bear River the ridge is not more than one hundred 

 to five hundred yards in width for a distance of three miles in a straight 

 line. In this distance are ten or twelve ridges of upheaval which both 

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