Diluvium. 163 



the grooves and correspondent ridge's may remain, although layer 

 after layer scales off. Yet the ridges will be liable to suffer rather 

 the most from atmospheric .agents ; and, therefore, in some rocks, 

 they will probably soon disappear. 



It may be well in this place to suggest a caution against mistaking 

 the structure of the rock as revealed by disintegration, for these dilu- 

 vial furrows. Some varieties of mica slate exhibit a surface extremely 

 resembling one mechanically grooved. But in that rock, the direc- 

 tion of these pseudo-grooves always corresponds with that of the lay- 

 ers of the rock ; and thus the deception may be discovered. But 

 sienite and greenstone, which contain segregated veins, sometimes 

 present cases that are very perplexing. One of these may be seen 

 on the top of Mount Tom, a few rods north of the signal staff, erected 

 for the Trigonometrical Survey of the State. The prevailing direc- 

 tion of the apparent furrows there, is nearly north and south; and 

 did they not run east and west within a rod or two of the spot, I 

 should have put down this as a genuine case of diluvial grooves. 

 But examination, after my suspicions were excited by this circum- 

 stance, satisfied me that it is only the internal structure of the rock, 

 that is here revealed by the unequal disintegration of the surface. 



But to return to a consideration of the diluvial grooves in the wes- 

 tern part of the State : I think it obvious, from the examples that 

 have been adduced, that the general direction of the waters there, as 

 well as in the eastern part of New York, must have been from north- 

 west to southeast. The two exceptions mentioned, I think may be 

 explained by their local situation, in consistency with this supposi- 

 tion. 



Now these furrows on Hoosac mountain, and in New York, are as 

 distinct as in other parts of Massachusetts : and, therefore, we must 

 consider them all as produced at the same epoch. Had there been any 

 great difference in the time of their production, especially had one 

 set of them been the result of the elevation of the strata, and the 

 other of the last deluge events that form almost the limits of geol- 

 ogical changes in point of time the oldest must have been lost, or 

 become obscure. Whatever difficulties attend the supposition, there- 

 fore, I think we must regard all these diluvial grooves in the State as 

 resulting from the same deluge. 



It would be easy to multiply examples of this kind of diluvial ac- 

 tion. But the cases that have been described, occurring as they do 

 in every part of the State, and frequently upon its highest mountains, 



