98 
ELEMENTS OF GEOLOGY. 
test the denuding power of the wind at points where run¬ 
ning water could never have exerted any influence. The 
waste eftected by wind aided by frost and snow, may not be 
trifling, even in a single winter, and when multiplied by cen¬ 
turies may become indefinitely great. 
Action of Ritnnmg Water ,—There are different classes of 
phenomena which attest in a most striking manner the vast 
spaces left vacant by the erosive power of water. I may al¬ 
lude, first, to those valleys on both sides of which the same 
strata are seen following each other in the same order, and 
having the same mineral composition and fossil contents. 
We may observe, for example, several formations, as Nos. 1, 
2 , 3, 4, in the accompanying diagram (Fig. 80): No. 1, con- 
Fig. SO. 
glomerate. No. 2, clay. No. 3, grit, and No. 4, limestone, each 
repeated in a series of hills separated by valleys vaiying in 
depth. When we examine the subordinate parts of these 
four formations, we find, in like manner, distinct beds in each, 
corresponding, t)n the opposite sides of the valleys, both in 
composition and order of position. No one can doubt that 
the strata were originally continuous, and that some cause 
has swept away the portions which once connected the 
whole series. A torrent on the side of a mountain produces 
similar interruptions; and when we make artificial cuts in 
lowering roads, we expose, in like manner, corresponding 
beds on either side. But in nature, these appearances occur 
in mountains several thousand feet high, and separated by 
intervals of many miles or leagues in extent. 
In the “ Memoirs of the Geological Survey of Great Brit¬ 
ain” (vol. i.). Professor Ramsay has shown that the missing 
beds, removed from the summit of the Mendips, must have 
been nearly a mile in thickness; and he has pointed out con¬ 
siderable areas in South Wales and some of the adjacent 
counties of England, where a series of primary (or palaBozoic) 
strata, not less than 11,000 feet in thickness, have been strip¬ 
ped off. All these materials have of course been transport¬ 
ed to new regions, and have entered into the composition of 
more modern formations. On the other hand, it is shoAvn by 
