THE HISTORY OF THE NORTH ATLANTIC 67 



somewhat dried up. It has a large and intensely hard stone 

 and kernel, a thin pulp made up of two layers, an inner, more 

 dense and dark-coloured, and an outer, less dense and lighter- 

 coloured. These constitute the under-crust. On the outside 

 it has a thin membrane or over-crust. In the process of drying 

 it has slightly shrunk, so as to produce ridges and hollows of 

 the outer crust, and this outer crust has cracked in some places, 

 allowing portions of the pulp to ooze out — in some of them its 

 lower dark substance, in others, its upper and lighter material. 

 The analogy extends no farther, for there is nothing in our 

 withered fruit to represent the oceans occupying the lower parts 

 of the surface, or the deposits which they have laid down. 



Here a most important feature demands attention. The 

 rain, the streams, and the sea are constantly cutting down the 

 land and depositing it in the bed of the waters. Thus weight 

 is taken from the land, and added to the sea bed. Geological 

 facts, such as the great thickness of the coal measures, in which 

 we find thousands of feet of sediment, all of which must have 

 been deposited in shallow water, and the accumulation of 

 hundreds of feet of superficial material in deltas at the mouth 

 of great rivers, show that the crust of the earth is so mobile as 

 to yield downward to every pressure, however slight.^ It may 

 do this slowly and gradually, or by jumps from time to time ; 

 and this yielding necessarily tends to squeeze up the edges of 

 the depressed portions into ridges, and to cause lateral move- 

 ment and ejection of volcanic matter at intervals. 



Keeping in view these general conclusions, let us now turn 

 to their bearing on the origin and history of the North Atlantic. 



Though the Atlantic is a deep ocean, its basin does not 

 constitute so much a depression of the crust of the earth as 

 a flattening of it, and this, as recent soundings have shown, 

 with a slight ridge or elevation along its middle, and banks or 

 terraces fringing the edges, so that its form is not so much 

 * Starkie Gardiner, Nature, December, 1889. 



