CRUSHED LEDGES. 89 



Still, at Newbury it is difficult to exclude the bent strata from those fractured, as to 

 their origin. 



One of us (C. H. Hitchcock) represents the overlying limestone at the Rutland 

 marble quarries to be very much fractured, so much so as to be useless as marble. 

 Some force a,cting at the surface seems to have done this work. Prof. James Hall, in his 

 Report on the New York Survey, has given a very instructive section of an extensive 

 disturbance of this kind near Niagara Falls, which nothing but a powerful lateral force 

 can explain. We have seen several similar examples at the red sandstone quarries near 

 Newark, in New Jersey, where the thick beds have been in some places broken into frag- 

 ments and crowded together like drift, while in other places the strata have been only 

 cracked and somewhat plicated. A similar case of fracture, without the removal of the 

 fragments much out of place, may be seen in a quarry at the north end of Mount Tom, 

 in Massachusetts. 



One of us, in 1850, found in the famous slate quarries of Llanberis, in North Wales, 

 that the laminae had been broken and bent down just as in Gruilford and Dummerston, 

 although on a less scale in Wales. Mr. Darwin and other English geologists have 

 described similar cases elsewhere. 



Here, then, we have a wide-spread effect indicative of a common cause, or causes. 

 Thirty years ago, when only the case at Gruilford was known to us, we shrunk from 

 assigning any cause. But twenty years ago, when the facts were multiplied, we regarded 

 the phenomena as the result of thick masses of ice resting upon the surface, and subject 

 to a horizontal movement. Either glaciers, or ice islands and icebergs, would answer the 

 conditions of such an agent, though where the force seems to have operated in different 

 directions in the same region, the ice island and the berg would most satisfactorily explain 

 the effects. Charles Darwin supposed that the bergs might have been lifted up by the 

 waves and then brought down upon the ledges like a vast maul. But great weight and a 

 powerful horizontal (onward or lateral) strain would be all that is necessary, and much 

 better explain such cases as those at Rutland, Newark, and Niagara, than Darwin's 

 gigantic battering ram. 



On visiting Bruce's quarry a few years ago, in the spring, we found unmistakable proof 

 that frost, getting between the layers of slate, and snow by its weight, had opened and bent 

 them down more or less, and for a time we were inclined to suppose that such might have 

 been the origin of the whole disturbance, which we believe was the theory ultimately 

 adopted by Dr. C. T. Jackson. But this cause is quite inadequate to explain such a case 

 as we have sketched above (Fig. 35) in Dummerston, and still more so to account for the 

 enormous downward pressure which at Willard's quarry in Gruilford and in Newbury has 

 thrown the strata to the depth of twenty feet into a zigzag form, or even crumpled them 

 together, and it applies not at all to the cases at Rutland, Newark, Niagara, and North- 

 ampton. Our final conclusion, therefore is, that the strata were first crushed and dislo- 

 cated by huge masses of ice, probably during the drift period, or in some cases even 

 earlier, while yet the layers retained some degree of plasticity, and that even up to the 

 present time frost and gravity have been carrying on the work of loosening and urging 

 downwards the fragments. 



In the northeast part of Pittsford, an interesting example of ledges broken up by some 

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