274 SAND-PLAINS OF BELGIUM. [Feb. 



of the Great Sahara. But there is not one geologist in a thousand 

 who would not say those beds of sand must have been at some time 

 an ocean bed. This will probably be admitted without question in 

 regard to the sand-plains of Europe and of Asia; but as it is with 

 them, so is it with the last-mentioned. 



The Sahara I cannot consider a land-formation of sand. There 

 is much, if I may not say everything, in its surroundings and its 

 conditions to indicate that at a time not very remote, geologically 

 considered, it was the basin of an inland sea. And in accord- 

 ance with this conjecture are the different schemes for converting it 

 into such again, by cuttings from the Mediterranean and from the 

 Atlantic Ocean, which have engaged the attention of scientific men 

 in the course of the present decade. In scientific statements in 

 regard to the extensive sand-plains in the north of Europe, their 

 deposit is generally attributed to diluvial action ; iu explanation of 

 which phrase I may mention that frequently in geological notices of 

 sand deposits we find sand spoken of as alluvial, others as diluvial, 

 the latter being such as have been spread out by water action such 

 as may be assumed to take place at the bottom of a sea, whether 

 inland or oceanic, the alluvial deposits being such as had been 

 occasioned long after by new currents where it had become dry 

 land, disturbing, removing, and depositing elsewhere what had thus 

 been spread out by the action of the sea. M. Pierre Tchihatchief, 

 while admitting that the large sandy surface of the Sahara suggests 

 at once a recently raised sea l^ottom, maintains that the immense sand 

 accumulations are of sub-terial and not of marine origin, — by which, 

 I presume, he means that an alluvial deposit from quaternary and 

 recent sand-stones was spread out on the basin of an inland lake. 

 I am strongly disposed to accept this hypothesis ; but whence 

 came the sand deposits which were thus redistributed ? I can only 

 answer, from the primeval sea. 



But how came the sand to be in the ocean basin ? Observation 

 leads to the conclusion that some may have been formed there ; that 

 some may have been borne thither by rivers of which it is 

 written that they all run into the sea; and that the supply produced 

 by the sea may be comparatively limited, and the supply carried 

 thither by the river comparatively great. 



Not only are rocks undermined by the waves and brought down 

 and broken up, but the sivash of the shingle, as it is moved hither 

 and thither by the advancing and receding wave, tells of col- 

 lision and friction, and the rounded form of the stones thus driven 

 against each other tells of the breaking off of particles such as those 

 of which sand is composed. But the action of the waves is limited 

 in space, and the quantity of sand thus produced is probably small 



