1894- CONTINENTAL GROWTH. 293 



there are grounds for believing that they may be chemically deposited 

 as well as organically separated. 



Orographic Relation between Mountain Ranges and New 



Land-areas. 



Leaving for future consideration the regional variations of level 

 which occur in the earth's crust like slow pulsations, and which do 

 not appear to be directly connected with sedimentation, we will briefly 

 examine the evidence pointing to the relation between mountain 

 ranges and new land areas. It is a pretty-well-established fact due 

 to the labours of Hall, Le Conte, Dana, and numerous other investi- 

 gators, that mountain ranges are built up out of great thicknesses of 

 sediment. Upon this phenomenon is based my theory of the origin 

 of mountain ranges by sedimentary loading and cumulative recurrent 

 expansion. 3 The evidence that mountain ranges are composed of 

 great thicknesses of sedimentary rocks, often with very little uncon- 

 formity between the rock-groups of which they are built up, is an open 

 book to anyone who takes the trouble to carefully examine the sections, 

 maps, and descriptions of any of the known mountain areas in any 

 part of the globe. It is true of the Rocky Mountains, the Andes, the 

 Himalayas, the Alps, the Caucasians, the mountains of the Turco- 

 Persian frontier as also of the older chains such as the Appalachians 

 and Urals, which have been greatly denuded. It will no doubt turn 

 out to be equally true of the Thian Shan and the great ranges of 

 Central Asia bordering Chinese territory ; but these have been so far 

 very little studied. 



An examination of the excellent geological map of the world 

 recording all the information up to date, which the labours of Jules 

 Marcou have given us, will show that the rocks comprising the newer 

 mountain chains, which are generally considered to have been 

 upheaved in Tertiary times, have a wide extension beyond the limits 

 of the main mountain-masses. Roughly speaking, the Cretaceous 

 and Tertiary may be said to occupy the half of Europe and a large 

 area of Northern Africa, together, doubtless, with the bed of the 

 Mediterranean Sea. It is just where these rock-groups are most 

 developed and underlaid by more or less conformable Mesozoic 

 groups of great thickness that the mountain-masses occur. This is 

 true even of the Apuan Alps as shown in Stefani's excellent 

 sections.'* These rock groups appear to extend from the Caspian 

 to the Himalayas, but further eastward we get largely into the 

 unknown. 



In North America, though we have not such full information as in 

 Europe, the Cretaceous appears to occupy, or did occupy (having been 



3 " Origin of Mountain Ranges " ; London, 1886.-^/50 see Outline of Mr. 

 Mallard Reade's " Theory of the Origin of Mountain Ranges," Phil. Mag., 1891, pp. 

 485-496. 



"• " Le Pieghe dello Alpi Apuane, contribuzione egli studi suU' origine delle 

 Montagne." Firenze : 1889. 



