CLASSIFICATION OF MOUNTAIN RANGES. 665 



A CLASSIFICATION OF MOUNTAIN RANGES ACCORD- 

 ING TO THEIR STRUCTURE, ORIGIN, AND AGE.* 



By WAEEEN UPHAM, 



OF THE TTNITED STATES GEOLOGICAL SURVEY. 



THE sea, in its vastness, reaching far "beyond the encircling 

 flat horizon, is a better symbol of infinitude and of eternity 

 than is the most majestic mountain range, lifting its serrated 

 forehead miles above the ocean-level and seeming almost to pierce 

 the sky. The sea itself, but no part of the land forming its shores, 

 has continued unchanged through the series of geologic eras. 

 " Time writes no wrinkle on thine azure brow 

 Such as creation's dawn beheld, thou rollest now." 



But on the land, no sooner have the subterranean forces up- 

 heaved a mountain, a plateau, a continent, or an island, than the 

 processes of subaerial erosion begin to contend against it. Rains, 

 frost and heat, chemical change, subdue the most enduring and 

 solid rock formations, dividing them with fractures, and pulveriz- 

 ing their masses and fragments to sand and clay, which gravita- 

 tion by the vehicle of running water carries down and away to 

 the sea, there to find rest until another uplift shall renew the 

 cycle of changes. " The mountain falling cometh to naught, and 

 the rock is removed out of his place." 



The form of mountains and of their ranges and systems is due 

 to the combination, in varying ratios, of constructive and de- 

 structive agencies. The first only seem necessary ; but the second 

 have generally been far more efficient to give the shape and out- 

 lines of all our mountains, excepting volcanoes. Constructive 

 forces have done work that may be compared to the quarrying of 

 the block of marble and bringing it to the artist's studio ; destruc- 

 tive forces, producing the present mountain forms, as they stand 

 before our vision, have done work like chipping away the greater 

 part of the marble block and chiseling it to the finished statue. 

 It will be convenient to speak of the constructive processes as 

 mountain -building, and of the destructive as mountain-sculpture. 



It is from observation and study of the geologic structure of 

 mountain ranges, the diverse rock formations of which they are 

 composed, and their attitude and relationship to each other, that 

 we discover and understand their origin ; how, by what agencies, 

 the mountains have been built and sculptured. Structure and 

 origin are thus very intimately connected and demand the same 

 division under classes and types. In this classification, when cit- 

 ing examples of each type, we can commonly note also their geo- 



* Read before the Appalachian Mountain Club, April 8, 1891, 



