GEOLOGICAL SURVEY OF THE TERRITORIES. 147 



described in as brief terms as we could, the character of the vast area 

 drained by the three forks of the Missouri ; we have shown that the 

 mountain ranges lie along the borders of the synclinal valleys, which 

 were originally the basins of fresh-water lakes. All these ranges have 

 a general trend north and south, or northwest and southeast, and yet 

 they are here and there connected by cross-chains, as it were, which 

 give origin to small branches. If we look on the map, (and every map 

 of this country now in existence is very imperfect,) we shall see the 

 three grand streams that constitute the three forks of the Missouri. 

 The main branches flow through valleys which now expand out to a 

 width of three to five miles, then close up in a deep gorge or caiion, 

 then expand out again into broad, fertile, grassy valley so with each 

 from mouth to source. These expansions, or broad valleys, have all been 

 lake-basins during the last portion of the Tertiary period, and perhaps 

 extended into the Drift or Quaternary. On either side, these valleys are 

 inclosed by more or less lofty ranges of mountains, broken here and 

 there by the entrance of some branch, or by some turns in the main 

 river cut through, and another range takes its place. Again, if we look 

 at a correct map we shall see that each one of these main rivers has 

 numerous branches flowing in from either side, and that many of these 

 branches have their small tributaries fed by the snows upon these 

 high mountain ranges. Each one of these principal branches, inclosed 

 by a range of mountains, is sometimes so low that I have called them 

 mountain hills. There is no doubt that these valleys are i>artly due to 

 erosion, but they are for the most part synclinal folds, and the inter- 

 vening mountain ridges are a wedge-like mass of Carboniferous limestone, 

 the beds inclining from both sides like the steep roofs of a house. Not 

 unfrequently the great mass of limestone has been sw^ept away, and the 

 ranges are less lofty and more rounded, exposing to atmospheric agen- 

 cies the metamorphic rocks, and here are located the valuable mines. 

 Sometimes, through the metamorphic strata, and even the sedimentary 

 rocks, the fluid interior has burst forth, forming a long line of high, 

 black, conical peaks, usually covered with perpetual snows. 



We may say of a large portion of Idaho and Montana that the surface 

 is literally crumpled or rolled up in one continuous series of mountain 

 ranges, fold after fold. Perhaps even better examples of these remark- 

 able folds may be found in the country drained by Salmon Eiver and its 

 branches, where lofty ranges of mountains, for the most part covered 

 with limestones and quartzites of the Carboniferous age, wall in all the 

 little streams. None of our published maps convey any idea of the 

 almost innumerable ranges. We might say that from longitude 110° to 

 118°, a distance of over five hundred miles, there is a range of mountains, 

 on an average, every ten to twenty miles. Sometimes the distance across 

 the range in a straight line, from the bed of a stream in one valley to the 

 bed of the stream in the valley beyond the range, is not more than five 

 to eight miles, while it is seldom more than twenty miles. From these 

 statements, which we believe to be correct, the reader may form some 

 conception of the vast amount of labor yet to be performed to explore, 

 analyze, and locate on a suitable scale these hundreds of ranges of 

 mountains, each one of which is worthy of a name. As we approach 

 the great divide or crest of the water-shed we might suppose that rocks 

 of very ancient date would be the only ones exposed, but those of more 

 modern origin prevail. Eocks older than Carboniferous are the excep- 

 tion. The crest of this water-shed is an irregular ridge from 7,000 to 

 8,000 feet above the sea, with here and there along the line, peaks or 

 groups of peaks 9,000 to 11,000 feet high. The lower portions of the 



