488 Mr. T. M. Reade on the Origin of Mountain-Ranges 



more folded and disturbed portions of the chain which often, 

 so far as the newer sediments are concerned, lie on the flanks, 

 the strata take on more gentle curvatures until, as in the case 

 of the Urals, the Appalachians, and elsewhere where ob- 

 servable, they become nearly horizontal, or only have dips 

 due principally to faulting. 



The Tertiary and Cretaceous rocks extend from the Alps 

 to the Caucasus and across the Mediterranean to the African 

 coast, and may lie far beyond, as little is known of the 

 geology of that part of the continent. They reappear in the 

 Himalayas, and may be continuously connected, though this 

 has not yet been proved. The same formations extend far 

 to the eastward of the Rocky Mountains and the Andes, and 

 most probably to the westward under the Pacific Ocean. 



The greatest ranges of the world have been elaborated in 

 Cretaceous or Tertiary times, and the connexion between 

 sedimentation and upheaval is here most striking. 



Sediments out of ivhich Mountain-Ranges have been elaborated 

 were laid down in Basins or Troughs formed by the 

 bending of the Eartlis Crust. 



The thickness of the rocks, mostly conformable, composing 

 some great mountain-ranges has been estimated by competent 

 geologists at from 8 to 10 miles. The bulk of the rocks, as 

 judged by their constitution, are usually considered by 

 geologists to largely indicate either a moderate depth of water 

 or actual shallow conditions. These rocks are intercalated 

 with others exhibiting signs of a more oceanic origin. All 

 the mountain-ranges mentioned may be pointed to in illustration 

 of this statement. There is thus evidence that regional 

 fluctuations of level in the Earth's crust have taken place on a 

 large scale often succeeded by, as in the case of the Coal- 

 measures, continued downward subsidence combined with 

 shallow- water conditions. 



It is evident, from these facts, that the great earth-troughs, 



to energetic denudation. He infers also that the developed sections of 

 such foldings are no measure of the original horizontal length of the beds 

 — a principle I have strongly upheld, and which is being conceded by 

 most geologists who have studied mountain-structure. The district 

 seems to be one in which the first principles of the dynamics of mountain- 

 building can be well analysed, as there is not such a complexity of causes 

 to be considered and discounted as in the more colossal disturbances of 

 the great mountain-ranges of the world. A few careful studies of 

 mountain physiography such as this by geologists who have the oppor- 

 tunity and are equipped with the necessary physical knowledge would be 

 of infinite service, 



