GEOLOGICAL SURVEY OF THE TEEEITORIES. 



69 



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terrace in tlie limestone for a half a mile below, forming a sort of contin- 

 uation of the isolated low ridge in the bottom just abovethe Gallatin. In 

 the second expansion of the valley 

 there is a broad bottom about two 

 miles wide. On the east side of 

 the valiey are quite thick tlepos- 

 its of the Lake period cut up into 

 ridges, which are weathered into 

 architectural forms like what we 

 have usually termed in the West, 

 '•bad lands." The lower portion 

 of these deposits is a kind of cal- 

 careous shale, passing by degrees 

 into an indurated sandstone capped 

 by a large thickness of conglom- 

 erate. This is made up to a great 

 extent of rounded masses of lime- 

 stone loosely held together by a 

 sand cement or with a whitish 

 marly paste. In many localities 

 in these deposits there are dikes 

 of basalt which seem to have been 

 formed during the existence of the 

 lake, and that the basalt had been 

 exposed by the wearing out of the 

 ravines which have been cut into 

 these modern deposits at a very 

 modern date. (Fig. 18.) For miles 

 along the high mountains that 

 border the river, hundreds of deep 

 canons or gullies, from three to six 

 miles long, are carved deep into 

 the sides. The modern beds are 

 nearly or quite horizontal, with no 

 ■evidence of disturbance since their 

 deposition, and they lap on to the 

 much-tilted strata of the older 

 rocks. There are here, as near as 

 I can estimate, about 2,000 feet of 

 more or less metamorphosed slates, 

 clays, and quartzites of all textures 

 and colors, but mostly thinly lam- 

 inated. Much of it is very slaty. 

 Here and there a dike is seen which 

 shows an efl'usion of melted matter 

 at some iJeriod subsequent to the 

 upheaval, ^o fossils could be 

 found, but I have no doubt that 

 they belong to the Potsdam group, 

 so well shown on the Gallatin, and, 

 indeed, the same beds are much 

 more changed. As we ascend the 

 mountain the compact gray lime- 

 stones, which are also of the Silu- 

 rian age, are well developed and, 

 above these limestones, full of well- 

 defined carbonileious fossils. (Fig. 



19.) How far to the northward these 



