208 EXPLORATION OF THE CANONS OF THE COLORADO. 
have been broken up or lost, and these fragments only remain to attest to 
the existence of such beds in some former time, and all stages may be ob 
served, from the beds the edges only of which have been broken up, to those 
that have only fragments remaining or have entirely disappeared. Another 
interesting fact has been observed, that these erratics or boulders are often 
found distributed somewhat in lines due to the undermining of lines of cliffs. 
Often where we have cliffs capped with a bed of lava, former and more ad 
vanced positions of these lines of cliffs can be recognized by the position of 
lines of lava fragments which are seen in the valley or plains in front of 
the cliffs. It will be seen that these local accumulations of material, due to 
the excess of erosion over that of transportation, greatly resemble the accu 
mulations of "the Drift." Especially is this true where I have studied the 
latter in the valley of the Mississippi, and I have been led to query whether 
it may not be possible to refer the origin of the Drift of the Valley of the 
Mississippi, in part at least, to some such action as this ; not that I question 
the evidence of extended glacial action in that region, but may it not be 
that this glacial action has only resulted in somewhat modifying a vast ac 
cumulation of irregularly bedded material, originally due to the fact that 
the grand base level of erosion had been reached by the running streams of 
that region, and hills and mountains had been degraded by having the ma 
terial of which they were composed scattered over lower lands, without being 
carried away by streams to the sea? 
All the mountain forms of this region are due to erosion ; all the canons, 
channels of living rivers and intermittent streams, were carved by the run 
ning waters, and they represent an amount of corrasion difficult to compre 
hend. But the carving of the canons and mountains is insignificant, when 
compared with the denudation of the whole area, as evidenced in the cliffs 
of erosion. Beds hundreds of feet in thickness and hundreds of thousands 
of square miles in extent, beds of granite and beds of schist, beds of marble 
and beds of sandstone, crumbling shales and adamantine lavas have slowly 
yielded to the silent and unseen powers of the air, and crumbled into dust 
and been washed away by the rains and carried into the sea by the rivers. 
The story we have told is a history of the war of the elements to beat 
back the march of the lands from ocean depths. 
