GREEN Mr 



CAVERN. 219 



he will find himself at the summit level of the two streams named above, while the Taconic range there 



culminates in Mt. Eolus, which shows on its east and south sides 

 strata of white limestone of immense thickness. Marble quarries 

 are opened in it at various heights, one as high as 1500 feet above 

 the valley. At this spot a large cavern opens into the mountain on 

 the almost perpendicular wall, and sloping downward in a westerly 

 direction, extends, no one knows how far (see Fig. 107), but it 

 probably has an outlet, on the west side of the mountain ; for it is 



obviously an old river bed, such as are common in limestone regions. The figure subjoined will give an idea 



of its situation. 



The question naturally arises, what has become of the surface over which the ancient 

 river flowed that wore out this cavern? And it seems rational to reply that it has been 

 worn away that is the valley below, 1600 feet deep, has by some agency or other been 

 worn out since that river ceased to flow. The only other supposition is, that the mountain 

 has been lifted up. It certainly has been subject to great disturbance, and probably has 

 been elevated ; but we apprehend not since the present configuration of the surface has 

 been produced. At least there is no evidence that Eolus has been subject to vertical 

 movements more recently than the other parts of Vermont. The disturbance appears to 

 have been anterior to the commencement of these erosive operations which seem to us to 

 have furrowed out most of the valleys of the State. 



Here, then, we have a deep, and for the most part a narrow valley, 50 or 60 miles long 

 in Vermont, and extending southerly still further across Massachusetts and Connecticut, 

 which seems to have been excavated in some way or other. At least if we admit that it 

 was done at Dorset to the depth of 1600 feet, we may presume that in its whole length it 

 was the work of erosion, since it is scarcely deeper in any other place. By parity of 

 reason the other deep valleys which inosculate with this, may be imputed to a similar 

 origin. To what agency shall we impute such a work? If we can answer this question 

 satisfactorily, the explanation will apply equally well to the other cases of deep excava- 

 tions which we have described at summit levels. 



We suppose the agency to have been partly oceanic and partly fluviatile. In another 

 place we have presented the evidence that this continent has been again and again 

 beneath the ocean, both submergences and emergences having taken place with extreme 

 slowness. The consequence would be, that every foot of the surface has been again and 

 again, and for ages exposed to the erosive agency of oceanic waves and currents. Suppose, 

 now, a mountain ridge, having a depression in its crest, to be slowly emerging from the 

 water. While the higher parts would form islands, the winds, the tides and the currents 

 would cause the water to rush forward and backward through the openings. If the same 

 waters were loaded with ice, this would help on the erosion. The channels thus begun 

 would become narrow straits at length, and when the waters had sunk low enough for the 

 formation of rivers, they might for a time at least pass through these straits and deepen 

 them. Raised still higher, these gulfs might become the starting place for rivers flowing 

 in different directions, and these might in time wear out valleys of great extent. These 

 processes, repeated several times over, might have accomplished the mighty work, which 

 we have imputed to them in Vermont, of ploughing out at length her deepest valleys. 



