GEOLOGICAL SUEVEY OF THE TEERITORIES. 57 



first peak to the east is about 10,000 feet, the second peak 10,500, aud 

 the third peak ia the range 10,000 feet. • This will afford some idea of 

 the general elevation of these mountains. On the east side the mount- 

 ains gradual]}' bend down to the valley, but are covered with a dense 

 growtli of pines. Far southward extends the valley of Henry's Fork — 

 a marvel of beauty and freshness. The upper portion, for an extent of 

 twenty to twenty -five miles in length and five to ten miles in breadth, is 

 like a meadow, covered with a luxuriant growth of grass; while flowing 

 from the lake and winding through the middle of ttie valley, receiving 

 on either side numerous branches, is Henry's Fork. Still farther south- 

 ward is a dense black mass of pines, and just on the dim horizon, more 

 than one hundred miles distant, is the range of mountains that forms 

 one side of the rim of the Snake Eiver Basin near Fort Hall. I^orth of 

 this is the wonderful Teton Basin, which is also like a meadow. To 

 the southeast the shark-teeth summits of the Grand Tetons are most 

 conspicuous aud clearly defined, rising so high above all other moantain- 

 Ijeaks that the}' stand isolated, monarchs of all. To the nortliea>st of 

 the Tetons there is a broad extent of table-land, with a general eleva- 

 tion of 8,000 to 8,500 feet, covered with a dense growth of pines. This 

 plateau is probably covered with volcanic rocks. On the east or north- 

 east is the Tahgee Pass, and Bannack Trail, which cuts through a range 

 of mountains, the highest peaks of which are 9,000 feet, down the east- 

 ward slope, to the pine table-lands about the sources of the Madison and 

 Yellowstone. Nearly all the rocks on the southeast side of the Tahgee 

 Pass are volcanic. Yet on the sides of the pass are a few outcroppings of 

 limestone. We know that the limestones are underneath the trachytes. 

 The area occupied -by the different kinds of rocks can only be shown by 

 colors on the geological map, which will be prepared in due time. On 

 the north side of Henry's Lake is the range of mountains which forms 

 the divide between the Snake and Madison Eivers, and through which 

 the Madison cuts its way in forming its Middle Caiion. Henry's Lake 

 is a fine illustration of a remnant, dating back j)robably to Pliocene 

 times, when all these valleys were filled with water, perhaps connecting 

 the drainage of the Missouri with that of the Columbia, and as the 

 waters subsided, formed the vast chain of lake-basins along all the im- 

 portant streams on both the Atlantic and Pacific slopes, of which our 

 l)resent lakes are only insignificant remnants. 



I have no doubt that the lowest strata of unchanged rocks about 

 Henry's Lake are Silurian, probably of the Potsdam group, but 1 looked 

 in vain for any traces of organic remains. The Carboniferous limestones 

 higher up were filled with characteristic fossils. I regard this as one 

 of the most interesting geographical points in the West. Within a cir- 

 cle of about fifteen miles in diameter there are four most important 

 passes in the Eocky Mountain divide, which may represent the four 

 points of the compass. The East or Tahgee Pass connects the Yellow- 

 stone ]^ational Park, the sources of the Madison, and the Yellowstone, 

 with the Pacific coast. It has an elevation of 7,063 feet. The second 

 may be called the North or Eaynolds Pass, and leads from the Snake 

 Valley, by waj of Henry's Lake, over a smooth, grassy lawn, into the 

 Lower Madison Valley. The third is the Eed Eock or West Pass, which 

 opens into the valley of the Jefiersou by way of Eed Eock Lake, aud is 

 as smooth and as easily traveled as the Madison Pass. The South or 

 Henry's Pass completes the circle, and is lower than either of the other 

 three. The ease with which railroads or wagon-roads can be constructed 

 across these great divides is almost incredible to one that has not made 

 them a subject of study, and the great area of valuable territory which 



