GEOLOGICAL SUEVEY OF THE TEEEITOEIES. 31 



compact in texture ; other portions rough, vesicular, much like the basalt 

 in Snake Eiver Basin. 



On the morning of June 29, we left the beautiful valLey behind ns, and, 

 traveling 9 miles north, crossed the water " divide" of the Rocky Moun- 

 tains. Od the west side of the road, for ten or fifteen miles, the rounded, 

 grass-covered hills prevailed, and over the surface, quartzite bowlders, min- 

 gled with some sandstones, were scattered thickly everywhere. In the sides 

 of the ravines were numerous bare spots, which revealed a deposit of yel- 

 lowish-brown sand. There is evidently a very extensive modern deposit 

 all over the belt of country which forms what I will call the water di- 

 vide — a belt from ten to twenty miles in width, in which the drainage 

 gathers full force on the one side toward the Pacific, and on the other 

 toward the Atlantic. The elevation along the " divide " is 6,480 feet. To 

 the west is a range of mountains reachiug up above the limit of vegeta- 

 tion, among the snows. We measured one of the high limestone peaks 

 and found it 9,704 feet ; but there were several others still higher far- 

 ther to the west, which must have been 10,000 feet high. These mount- 

 ains are concealed high up around their sides with the drift deposit 

 mentioned above, so that their examination is rendered quite diflicult. 

 The mountains, so far as we could examine them, seem to be composed 

 of a great thickness of carboniferous limestones, capped with quartzite 

 and quartzitic sandstones. The first range has four prominent cones, 

 with several smaller ones, thewhole having a general trend about north 

 and south, with an inclination to the west 25°. On the east side of the 

 road were high, ridge-like hills, capped with basalt, all inclining to a 

 moderate angle southward toward Snake Eiver. Wherever any of the 

 branches of Dry Creek cut through the grass-covered hills, or ridges, 

 caiLons are formed with vertical basaltic walls. This igneous rock 

 seems to be very homogeneous in composition, except that some por- 

 tions may be more compact in texture than others. The surface of the 

 whole country is exceedingly picturesque, diversified by lawn, terrace, 

 ridge, and rounded hutte, with most beautiful grassy ravines. Where 

 the drift deposits are not too uniform and thick, we find exposed here 

 and there outcroppings of a yellowish calcareous sandstone, which is 

 probably of the age of the lignite beds of the West. No indications of 

 coal were observed, but leaves of deciduous trees, like those found in 

 the vicinity of the coal-beds in other places, were found here. These 

 sandstones form long ridges, inclining east about 10°. The rock is more 

 or less firm and compact 5 some of it is a greenish quartzite. Here and 

 there, on the summits of the ridges, are beds of basalt, showing igne- 

 ous outflow at a modern date. Indeed these basaltic caps on the hills 

 have presented many connected sections for examination which would 

 otherwise have been obscure, and fragmentary from erosion. Far 

 to the west may be seen range after range of mountains running 

 nearly north and south; as they extend down into Snake Basin 

 they seem to run out into the plain, so as to present an echelon appearance. 

 The ranges, so far as we can see, are the eastern portions of some 

 great central axis, which may be the Salmon Eiver Eange. I have 

 not been able to extend my observations so far west ; but the ridges, 

 so far as I could examine them, of which there were a number ex- 

 tending over a belt of fifty miles in width, appear to incline east- 

 ward. The abruj)t sides of the west, the sloping sides on the east, 

 the force as well as the material which have modified and given form to 

 the surface, must have come from the west, inasmuch as on the western 

 or abrupt sides of the mountains and hills th6re is the greatest accumu- 

 lation of drift-bowlders. The loftiest portions of the ranges seem to have 



