HEAD OF BEAR RIVER. 328 



formed of the same quartzitic material, and having been found in a 

 position which would hardly admit of its having come from any other 

 beds, except under the rather improbable hypothesis that an Indian had 

 placed it there. This is a half of a ribbed brachiopod, which has been 

 described by Messrs. Hall and Whitfield as Spirifer imbrex. From the 

 ddbris-piles in the basin was also obtained a quartz pebble, containing the 

 impression of a Crinoid column. These, with the Spirifer cameratus, from 

 near Geode Canon, already mentioned, constitute the sum of the somewhat 

 meagre palseontological evidence obtained as to the age of the quartzite beds 

 of the Uinta Range; though it is worthy of remark that in the quartzite 

 beds in general, as developed along the line of this survey, scarcely any 

 organic remains have been found. 



The bottom of the upper basin, directly under Mount Agassiz, 

 shows quite a variety in color as well as in bedding : heavy beds of 

 white quartzite divided by jointing planes into huge cuboidal blocks, 

 pale-green solid quartzites, containing conglomerate pebbles up to the size 

 of an egg, and dull-brown ferruginous beds, which are hardly compact 

 enough to be called a quartzite, but are rather an indurated sandstone. 



A partial anal3^sis of one of these white quartzites gives 98^ per 

 cent, of silica, the remaining constituents being iron and alumina. The 

 rocks forming the summit, extending for three or four miles on either 

 side, are in the position of a low flat arch. The summit rocks are nearly 

 horizontal. Those to the south dip about 5° south, and those to the 

 north about 8° north. The canon of Bear River descends toward the 

 north more rapidly than the dip of the strata for about six or seven miles, 

 when the beds are suddenly broken and flexed over to a dip of about 45° 

 to the north. From the broken and dislocated condition of this region of 

 flexure, it is impossible to get at the true relations of the steeper-dipping 

 part and the nearly horizontal beds higher up the canon ; but there is appar- 

 ently considerable vertical displacement, and the steeper-dipping beds seem 

 to have fallen down, so that, in estimating the thickness, it would not do to 

 add to the thickness of the upturned beds that which is exposed in the 

 horizontal ones. At least 4,000 to 6,000 feet of quartzites are exposed in 

 the steeper-dipping series, and 3,000 to 4,000 in the horizontal beds. Over- 



