SURFACE OF THE GLOBE. 45 



it, but which are found in penetrating some particular 

 stratum, giving rise to the wells commonly used for 

 procuring water in countries of low elevation. 

 Throughout the whole mountainous range of Scot- 

 land, springs are rare, nor does any one of great mag- 

 nitude exist ; all the great rivers of that country being 

 collected originally from those superficial mountain 

 torrents that proceed from the hourly rains which fall 

 on their innumerable elevated sources. In the com- 

 paratively low lands of England, on the contrary, they 

 abound ; while those of the Thames and other rivers 

 of that country, are testimonies of the size and power 

 with which they break forth, far from the declivities 

 of mountains. 



There is more truth in the observation that, where 

 they do abound, they will be found to regard the in- 

 clinations of the strata ; breaking out at the foot of 

 that declivity which is formed by the dip. Thus well- 

 diggers are directed in their search ; as they also are 

 by observations on the rocks or substances, of which 

 the several strata are formed. In this case, the water 

 finds its way, chiefly, between two strata, of which 

 the lower is impermeable to it. It has been often re- 

 marked that some particular rocks abound in springs, 

 while, in others, they are rare or wanting ; and this, 

 it will shortly be seen, depends chiefly on the dispo- 

 sition or existence of fissures. It has been said that 

 they were common in the trap rocks ; but, in Scot- 

 land, that rule does not hold good. Thus also, in 

 many parts of the Gneiss of Scotland, springs are 

 scarcely known ; whereas, in the island of Guernsey, 

 in the same rock, they burst forth in a thousand 

 places. Such assertions must be added to the endless 

 examples of fallacious generalization. Throughout 

 our own island, it may be observed, that they are not 



