SPRINGS. 145 
great attractors of clouds and vapour,* and the more 
so in proportion to their size and height, so that we 
reasonably regard our central, primitive, rocky dis- 
trict as the great source of the river water which 
descends to us, independently of the connexion 
which may subsist sub terra between it and the 
ocean. 
Springs are very abundant with us, except in 
limestone tracts; in slate they break forth with 
great freedom on account of the frequency of river 
currents, and the ease with which water traverses 
the substance of this rock, but limestone being 
cavernous, the water penetrates by the cracks and 
separations of its beds to the caves as far down as 
the level of any adjacent river, where it meets in all 
probability some spring of water from the stream, 
or to some other hollow which by its freedom from 
joints may act as a natural reservoir. In this way, 
the inhabitants of limestone districts not near any 
river, are greatly distressed for water, but should a 
mass of slate project into this tract as is extremely 
common, water may in all cases be readily obtained 
at a slight depth, particularly if a stream be adja- 
cent. The contrast between lime and slate with 
regard to the power of retaining moisture near the 
surface of the earth is readily seen in our lengthened 
droughts of summer, the limestone lands speedily 
displaying a burnt herbage, and the slate lands 
retaining a great proportion of their fresh green, a 
clear proof of the extent and utility of terrestrial 
exhalations. 
* Tavistock is situated at the foot of the junction of two ranges 
of hills, and is accounted one of the most rainy places in the 
kingdom. The moor altogether is under the baneful influence 
of a very humid air through all the months but the hottest. © 
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