360 THE CHASMS OF THE COLORADO. 











the acids in the water now dry, now wet, is it a wonder that 
they are covered by a coat softer than the interior of the 
rock, which is readily ground off or dissolved by the stream? 
The rusty coating of iron arises from the same causes, anl. 
yields in the same way. when exposed to similar infos 
until the hard metal has entirely disappeared. 
The lofty ledges themselves are constantly oranti 
finer dust swept away by the winds, and the heavier 
plunging to the bottom. Every rain carries away, in sol 
tion, the dust which the winds have spared, and a portion 
the softened outer-coxtings of the stones. l : 
Watch the bottom of any fast-running rivulet, you 
see a moving cloud of the finest particles, and under 
larger pieces rolling confusedly onwards. The large 
are slowly but surely wearing themselves away, and 
moving cloud is the result of this grinding. Thus it is thi 
nearly all the stones found in eee are pebbles. 
first broken away from the parent rock they must have #4 
sharp edges like any other fragment. Have you ge 
found a piece of a bottle in the bed of a stream, with th 
edges nicely smoothed, and the sides scratched and 
like ground glass? They are quite common, and show how : 
pebbles are made with perfect accuracy. ik 
Quietly and almost imperceptibly the tireless waters Wi e 
except when heavy rains or spring freshets, 
colored with their burden of dust “and dissolved rock, aie : 
even large boulders and destroy well-known land del 
The ability of water to handle rocks of any size, pro” pe 
it is deep enough and swift enough, is unquestioned. “i 
Au Sable River, where the inclination of the shelving e 
which formed the bed was not over two or three eae ; 
the depth more than eighteen inches, I have mys® if, pr : 
aid of a lever, rolled into the current great pieces of heard . 
stone, three or four feet long and a foot thick, ed | 
their heavy rumbling over the ledge as they were 
niay, Among the shales, limestones, and panier — 



