GLACIO-AQUEOUS ACTION IN NORTH AMERICA. 189 



this passage from the top of the mountain. And so in respect 

 to several others of the deeper valleys, they may have existed 

 previous to the exertion of this force ; and yet, where we find a 

 valley running obhquely across the ridge, it is difficult to impute 

 its commencement to any other agency. Is it not perfectly obvi- 

 ous, also, that currents of water never could have begun such 

 valleys ? For instead of ploughing their way obliquely along 

 the sloping edges of an excessively hard rock, they would have 

 been turned along its sides. But suppose a mass of ice, wide 

 enough to fill the valley of the Connecticut, to be urged over the 

 top of this mountain, with bowlders frozen into its under surface. 

 The consequence would be, since these gravers could not be 

 crowded either to the right or the left, that they would cut their paths 

 along whatever surface they were urged over. Parallel furrows 

 being thus begun, the currents of water would be diverted into 

 them, bringing along perhaps smaller fragments of ice, and thus 

 would they be deepened in the course of centuries, as the moun- 

 tain continued to rise, or the water to fall. Nor would the work 

 cease until the present configuration of the surface had been pro- 

 duced. I confess I can conceive of no other mode in which the 

 erosions on this mountain can be explained ; and although not 

 entirely free from difficulties, this theory carries with it an air of 

 probability. I can conceive no reason why such examples are 

 not common, except that in few places would glacio-aqueous 

 currents continue to operate so long as in this valley, and few 

 mountains are so favorably situated for receiving and retaining 

 the evidence of their action. I regard this case as affording very 

 conclusive evidence, first, of the great length of the glacio-aqueous 

 period ; and secondly, of the insensible manner in which glacio- 

 aqueous passed into alluvial agency. I do not mean that this 

 period was long, compared with many others which geology 

 reveals. But we have proofs here beyond all question, that 

 glacio-aqueous action could not have been the result of any 

 transient overflow of water and ice ; and that centuries at least 

 must have been occupied in such erosions. 



