140 KOSS — ON PAEALLEL LmES OF ELEVATION* 



and west, form almost impassable barriers to tbe migration of many 

 plants and animals, on account of the low temperature everywhere 

 prevailing at a considerable elevation above the sea-level. The 

 Himalaya mountains present perhaps the best illustration. As the 

 more important lines of depression are in regions covered by the 

 sea, these also serve as barriers to the migration of most land plants 

 and animals. Thus the narrow seas separating Asia from Australia, 

 separate regions whose fauna and flora are as unlike each other as 

 we might expect to find those of different planets. Scarcely less 

 relatively important have been the effects of the more important 

 lines of elevation and depression on the development of the human 

 race, as these chiefly have determined the migrations and nationali- 

 ties of mankind. 



" Mountains interposed 

 Make enemies of nations, who had else, 

 Like kindred drops, been mingled into one," 



The course of civilization has been along the subzone of 

 Peninsulas belonging to zone No. 2, on the south-west of Asia- 

 Europe ; and our American cousins would say thence across the 

 Atlantic to the Appalachian subzone, also of zone No. 2. Not 

 only is inter-communication by the more primitive methods much 

 more feasible along the prevailing lines of elevation of any region, 

 but these also usually determine the location of railways and 

 canals. The Caledonia canal constructed along a line of depres- 

 sion of zone No. 4, may be taken for an example. It would be 

 easy to show the great importance for the purposes of civil engineer- 

 ing, of an accurate knowledge of the lines of elevation and dej^ression 

 of any country, nor is the importance of such knowledge relatively 

 any less for military purposes. Zone No. 1 seems to date, as to 

 the elevation of much of it above the sea, to the close of the 

 Secondary or Mesozoic period ; zone No. 2 from the close of the 

 Paleozoic, and zone No. 4 from the close of the Azoic period. It 

 is probable that each zone, in its turn, had an apparent development 

 comparable to that of zone No. 1 at the present day — giving 

 approximate continuity to the land surface of the earth. That such 

 is the case may, I think, be proved from the distribution of existing 

 plants and animals and of fossil remains, but the limits of a paper 



