168 THE STOR7 OF THE EARTH AND MAN. 



other metals, to enrich the copper slate and its associ- 

 ated beds. It is also to be observed that the alkaline 

 springs and waters which contain carbonate of soda, 

 very frequently hold various metallic salts; so that 

 where, owing to the action of such waters, magnesian 

 limestone is being deposited, we may expect also to 

 find various metallic ores. 



Let us sum up shortly this history. We have fold- 

 ings of the earth's crnst, causing volcanic action and 

 producing limited and shallow sea-basins, and at the 

 same time causing the evolution of alkaline and metal- 

 liferous springs. The union of these mechanical and 

 chemical causes explains at once the conglomerates, 

 the red sandstones, the trap rocks, the magnesian lime- 

 stones, the gypsum, and the metalliferous beds of the 

 Permian. The same considerations explain the occur- 

 rence of similar deposits in various other ages of the 

 earth's history; though, perhaps, in none of these 

 were they so general over the Northern Hemisphere as 

 in the Permian. 



From the size of the stones in some of the Permian 

 conglomerates, and their scratched surfaces, it has 

 been supposed that there were in this period, on the 

 margins of the continents, mountains sufficiently high 

 to have snow-clad summits, and to send down glaciers, 

 bearing rocks and stones to the sea, on which may 

 have floated, as now in the North Atlantic, huge ice- 

 bergs.* This would be quite in accordance with the 



* Ramsay has ably illustrated this in the Permian conglomer- 

 ates of England. 



