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Portland and its Vicinity* 331 



other places ; but in these spots It is most abundant and 

 well marked. 



/ 



Diluvium 



In examining the geology of Massachusetts, I found, in 

 every part of it, abundant and incontrovertible evidence 

 of a powerful rush of waters over its surface from the 

 north and northwest. I ofien^ and almost always with 

 success, applied this fact to direct me in tracing boulders 

 to the rock from which they were detached. When I 

 went into Maine, with no knowledge of its geology, I 

 undertook to apply the same principle- From Casco 

 river to Portland, on Cape Elizabeth, and the islands in 

 Casco Bay, the rocks in place, I found, were all some 

 variety of slate. But the boulders scattered over the 

 surface were nearly half gneiss ; and I did not hesitate to 

 predictj with great confidence, that a few miles to the 

 north, this rock would be found in place. The sub- 

 joined map will show how well verified was this predic- 

 tion . 



The vicinity of Portland is not remarkable for any 

 extensive accumulations of diluvial detritus; I mean, 

 compared with other parts of our country; with the 

 eastern part of Massachusetts, for instance. The penin- 

 sula itself, on which the city stands, affords perhaps as 

 good examples of such detritus as I met with. The 

 northern and southern extremities are elevated above the 

 general level of the city, by deposites of diluvium. The 

 boulders here are chiefly gneiss and granite; the slates in 

 the vicinity being among the most unyielding of all rocks. 

 Now whoever is in doubt whether there are any marks 

 of diluvial action in the region of the city, let him stand 



