I 



Portland and its Vicinity. 333 



occur, however, not more than a mile or two from the 

 shore; as the rock beyond that distance is so changed 

 in its characters, that disintegration has obliterated the , 

 grooves. The same is true in respect to the gneiss 

 region generally. At the spot that has been described, 

 a little east of the northern extremity of the toll bridge, 

 leading from Westbrook to Portland, we find, both on 

 the slate and the trap rock, some good examples of these 



^ 



grooves. On the road to' Yarmouth I observed others, 

 about two miles from the city. But I found them at 

 length occurring so frequently, that I ceased to keep notes 

 of their location. 



In all the above cases, except perhaps that in Elm 

 street, the course of the grooves makes so large an angle 

 (from 50*^ to 70^) wuth the direction of the strata, that 

 there is little danger of confounding them with the 



grooves resulting from the unequal hardness of the suc- 

 cessive layers of slate, whereby some of them disintegrate 

 faster than others, and thus produce ridges and depres- 

 sions. In Elm street, the grooves resulting from both 



^ 



these causes come much nearer to a coincidence than in 

 other places. Still, I am confident that even there, some 

 divergence may be seen between them. It cannot be 

 expected, however, that diluvial grooves will be as dis- 

 tinct in the streets of a city, where they are continually 

 passed over by animals and men, as they are in the coun- 

 try. I was surprised to find them in the city at all.^ 

 The striking uniformity in the direction of the elevated 



Portland, is another 



circumstance 



these grooves. For where the direction is liable to 



ty rocks, within a few feet, 

 especially, is liable to make 



mistakes. 



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