J 



Portland and its Vicinity* 323 



country, is a ledge of talcose slate, dipping southeast only 

 20^ ; the least inclination that I have met with in the slate 

 rocks around the city. Here, in the edges of the strata, 

 we see thin veins of a peculiar variety of trap, which con- 

 tains more or less of mica, and which, in fact, seems to 

 he rather intermediate between slate and greenstone, 

 althoutrh its schistose structure is obliterated. In some 



O ^ 



places near this spot, which forms the shore of the bay, 

 the layers of talcose slate are removed, and the surface of 

 the trap is exposed ; and I noticed one or two narrow 



an 



A little nearer to the bridge, however, where the edges 

 of the talcose slate are exposed, I noticed perhaps the 

 most instructive example of these trap veins. The fol- 

 lowing sketch, showing the edges of the slate with the 

 included vein, will convey an idea of its peculiarities. 

 The dip of the strata here, as measured by the clinometer, 

 is 28° S. E. and the layers are very regular, running 

 northeast and southwest. The three portions of trap 



same 



left hand towards the right, the portions taper gradually ; 

 a being six inches thick, h four mches, and c three inches : 

 the latter terminating abruptly, so that were h and c to be 

 brought into a line with a, the whole would form an unin- 

 terrupted vein. Yet the layers of the slate do not ex- 

 hibit any fracture or displacement corresponding to the 



