247 Geology and Botany of Northern Pacific Railroad. 



ing to this coal formation, consist of a series of cascades having 

 an aggregate height of over 200 feet ; the lower fall is 98 feet, 

 the next 25, the next 40, the next 20, etc. They occupy the 

 whole breadth of the river, which is here about 1500 feet ; and 

 as the volume of water is large, they are exceedingly beautiful 

 and also furnish a water-power rivalling in magnitude that of 

 Niagara, and far more available. 



GEOLOGY OF THE BELT MOUNTAINS. 



The streams which flow into the Missouri from the Crazy and 

 Belt Mountains, form valleys which are remarkably picturesque 

 and of great geological interest. The coal-basin to which I 

 have referred is underlain by palaeozoic limestones more than 

 two thousand feet thick. These rise toward the south, where 

 they rest upon the Cambrian and Archaean nucleus of the 

 mountains. Deeply cut by the draining streams, they form the 

 walls of a series of narrow valleys or cafions, which, though less 

 impressive in magnitude, are more beautiful than those of the 

 Colorado. The limestones are sometimes blue, more generally 

 cream-colored, and lie in massive beds of 100 to 200 feet in 

 thickness ; these form a series of steps in the precipitous walls of 

 the valleys, from which project spires, castles, fortifications, 

 and other colossal imitations of human architecture. The light 

 cream tint of the prevailing limestone contrasts charmingly 

 with the dark green of the fir-trees that crown the summits and 

 cluster in picturesque groups wherever they can find a foothold 

 on the declivity. Add to these elements a variety of minor 

 plants, which with varied colors decorate the cliffs, and the 

 whole forms a combination which in beauty surpasses anything 

 that I have elsewhere seen in somewhat extended wanderings 

 through the far West. 



Cutting through the limestones and in places the coal-bearing 

 rocks, are eruptive dykes of three distinct kinds, which Mr. J. 

 P. Iddings has been kind enough to examine for me microscopi- 

 cally. He reports them to be, first, a typical augite-andesyte, 

 which forms the Bird Tail Divide and the upper portion of 

 " Square Butte," a conspicuous landmark on the west side of the 

 Missouri ; second, a true trachyte, with large crystals of feldspar. 



