544 THE JOURNAL OF GEOLOGY. 



But first of all I must define my subject. A mountain range 

 is a single mountain individual — born at one time (monogenetic) 

 i.e., the result of one — though it may be a prolonged — earth-effort ; 

 as contra-distinguished on the one hand from a mountain system 

 which is a family of mountain ranges born at different times 

 (polygenetic) in the same general region ; and on the other from 

 ridges and peaks which are subordinate parts — limbs and organs 

 - — of such a mountain individual. Now a theory of mountains is 

 essentially a theory of mountain ranges, as thus defined. In all 

 that follows, therefore, on the subject of mountain structure and 

 origin, we refer to mountain ranges. 



STRUCTURE OF MOUNTAINS. 



The origin of mountains is revealed in their structure. We 

 must, therefore, give briefly those fundamental points of structure 

 on which every true theory of origin must be founded. 



i. Thickness of Mountain Sediments. — The enormous thickness 

 of mountain strata is well known, but it is impossible to over- 

 state its fundamental importance. We therefore give some strik- 

 ing examples. The Palaeozoic rocks involved in the folded struc- 

 ture of the Appalachian, according to Hall, are about 40,000 feet 

 thick. The Palaeozoics and the Mesozoics in the Wasatch, accord- 

 ing to King, are about 50,000 feet thick. The Cretaceous alone, 

 in the Coast Range of California near the Bay of San Francisco, 

 according to Whitney, are 20,000, and in Shasta county, accord- 

 ing to Diller, are 30,000 feet thick. The Mesozoics and Ter- 

 tiaries of the Alps, according to Alpine geologists, are 50,000 

 feet. 1 The upper Palaeozoic and Mesozoic of the Uinta, accord- 

 ing to Powell, are 30,000 feet. These are conspicuous examples, 

 but the same is true of all mountains. 



It might be objected that these numbers express the general 

 thickness of the stratified crust everywhere — only that in moun- 

 tains the strata are turned up and their thickness exposed by 

 erosion. But this is not true. For in many cases the strata may 

 be traced away from the mountain ; and in such cases they always 

 thin out as distance increases. For example, the 40,000 feet of 

 1 Judd : Volcanoes, p. 295. 



