SUPERFICIAL DETRITUS. 
.331 
hundred more to touch the surface of the next limestone above, and so on to the end of the 
series. This objection, however, can be met by supposing the country gradually rising from 
the water, and that the highest parts were first scored, and the lower ones afterwards. But 
if we take this view, we then make the admission that the great inequalities of the country 
were previously existing ; and if these were made, we want no farther power to furnish the 
explanation we seek; for the same power which excavated a deep valley in a determinate 
direction, if more diffused in its operation, may have grooved and polished the strata over wide 
areas. 
The countless numbers of inconceivably fine striae upon the surfaces of the limestones, many 
of which are only visible by a magnifier, seem a strong objection to the theory that these 
phenomena have been produced by ice floes; and this fact of itself seems to me conclusive 
testimony against it. The lower surfaces of these icebergs are confessedly very irregular, and 
from the falling down of portions from above, the equilibrium is often destroyed, and the mass 
turns partially or entirely upside down. The fine strias and polished surfaces are more like 
what is produced when one even surface is moved over another, having sand or gravel be¬ 
tween the two; indeed, not very unlike the preliminary polishing of marble when the motion 
is all in one direction. It seems impossible that a mass of ice, with fragments of rock set in 
it, could have pressed so closely as to have produced such an effect. 
The polishing and striating of surfaces of limestone and other rocks, no harder than the 
sandstones of the Fourth District, is, after all, no process which requires such tremendous 
force as is sometimes called into action ; though if great force be applied, it would, doubtless, 
break up the strata, and still leave a striated surface below.* 
Another objection to this view is in the oblique furrows, which often diverge from the regu¬ 
lar course. Had all these been produced by fragments, like gravers, fixed in a mass of ice, 
no such furrows could have been made ; and if we maintain that these were worn by loose 
masses on the surface, which were moved by contact with the ice, then they are as capable 
of making the same impressions if moved by any other force. 
There is also another fact worthy of notice, which is that the vertical faces of joints, when 
much separated and nearly coinciding with the direction of these grooves, are polished or 
striated, in the same manner as the surfaces. Hundreds of instances can be observed near 
the outcropping edges of the Niagara limestone ; but this is readily understood by any one 
who has observed the chinks and fissures in harder rocks along the sea shore, which are 
similarly polished by the washing in of sand and pebbles by the advancing and retiring waves. 
I have seen a quarry at Lockport, the entrance to which was along the surface of a stratum in the direction of the dip; 
the superior strata had been removed, and this surface left in its natural state. After drawing stone from the quarry, on the 
common stone-drag, for a few weeks, the surface of the stratum became worn smooth and striated, and in some places nearly 
polished. This was done, merely by the fragments ground between the wood of the drag and the stratum below, as it 
moved over the surface. In this instance, there were few fragments or pebbles of any other rock than the limestone. 
42 
