GEOLOGICAL SURVEY OF THE TERRITORIES. 155 



posits in the form of rather compact tufa. On either side of the river 

 the high mountain hiils are composed of quartzites and Carboniferous 

 limestones. 



About fifteen miles above Soda Springs the river cuts through a vast 

 thickness of thin shales, varying in thickness from one-twentieth of an 

 inch to an inch, averaging about one-eighth of an inch thick, resembling 

 the Green Eiver shales on the Union Pacific Eailroad. They are mostly 

 horizontal, but occasionally incline 3° to 5°. They reach a thickness of 

 500 to 800 feet and appear to pass up into variegated beds of light- 

 gray aad pink sands and clays in this valley, resembling those of the 

 Wahsatch grouj) west of Port Bridger, By looking at the map it will 

 be observed that the valley of Green River is only about sixty miles to 

 the eastward, while southward the variegated beds are found filling up 

 the inequalities of the surface of the older rocks as far as the eye can 

 reach, on either side of our road to Evanston. The appearance of the 

 large mass of shales in the valley of Bear Eiver is not easily accounted 

 for, and they do not appear to conform to the older rocks. No fossils 

 could be found in the shales, and all that I can say of them is that they 

 appear to be of modern Tertiary age, and that in the scooi3ing out of the 

 valley they seem to have escaped the general erosion. About fifteen 

 miles below Soda Springs, are some thick local deposits of the white lime 

 stone, very compact and hard enough for building material or lime. This 

 fact is mentioned to show that these spring deposits, whether hot or cold, 

 extended far back into the past, at least to the Pliocene period, like 

 those iu the Yellowstone Valley. I have no doubt, however, that the 

 springs of Bear Eiver Valley were originally hot, perhaps some of them 

 geysers at a former period. 



The only method which I could take to ascertain the general geology 

 of the mountains on either side of the valley was to follow up the gorges 

 worn out by some of the little mountain streams. Bast of Bennington 

 the quartzites are well exposed, covering the side and summits of 

 the mountains and inclining at various angles towards the valley. 

 These quartzites, although so very hard and compact, have a brit- 

 tle fracture, and the sides and base of the mountains are covered 

 with vast quantities of the debris. Pollowing ^long the base of the 

 mountains, the limestones soon rise from beneath the quartzites, and at 

 Joe's Gap, near the town of Bennington, there is a gorge in the side 

 of the mountain that forms a remarkably clear section of the strata. 

 The little stream that carved out the gorge is now entirely dry, and 

 must be supplied in the spring by the melting of the snows. The gorge 

 itself is about 300 feet wide, with nearly vertical walls 500 feet high. 

 The upper 200 feet of strata are very massive, yellowish-gray, hard, and 

 quite pure limestone. The lower 300 feet are composed of layers, vary- 

 ing in thickness from an inch to 2 feet, and very regular. The rock is 

 very hard, tough, bluish or steel-gray, calcareous mud, with all the 

 peculiar markings of a shallow-water mud-deposit. Possils are abund- 

 ant in the limestones. The entire mass flexes over the sides of the 

 mountain, v/ith a curve toward the top, inclining 10° to 15°, and at the 

 base 20° to 30°. Of course, the strata ijass beneath the valley, and rise 

 again on the opposite side. Bear Eiver Valley is a synclinal depres- 

 sion. To the eastward a series of three synclinal folds may be seen, 

 extending nearly to Green Eiver, filled up, in some instances, with the 

 variegated beds of the Wahsatch group. Above Bennington the val- 

 ley begins to expand and forms a wide, marshy flat, with a soil com- 

 posed of rich, black earth, sustaining a thick growth of coarse grass. 

 There is no timber along the river except willows, and the high hills 



