Portland and its Vicinity. 311 



not quite so much carbonaceous matter in this slate, as 

 at first sight we might suppose. 



The most distinct and extensive stratum of this rock in 

 the vicinity of Portland, is on Cape Elizabeth. On the 

 north, as may be seen on the map, it extends to Hog 

 Island ; where, on the west shore of Diamond Cove, it 

 may be examined to advantage. In a southwest direc- 

 tion it probably extends across the whole Cape to the 

 ocean ; though I have not traced it so far. But the 



+ 



rocks of all that region are remarkably regular and con- 

 tinuous ; so that the geologist can apply analogical con- 

 siderations with great confidence, where direct evidence 



is wanting. 



On Jewell's Island — a very interesting spot for the 

 geologist— this rock forms a stratum of considerable 

 width, running through the central parts of the island, as 

 may be seen on the map. I have reason to suppose that 

 it exists In other places around Portland : but I have not 

 examined them carefully enough to justify me in repre- 

 senting them upon the map. 



Should it be found, in going northeasterly from Port- 

 land, that the rocks pass gradually into decided argilla- 

 ceous slate, then perhaps, it would be proper thus to 

 denominate this plumbaginous mica slate ; or rather to 

 regard it as forming an mtermediate link between mica 

 slate and clay slate. But so far east as I went, I per- 

 ceived no progress towards a change into argillaceous 



and I think I can perceive 



examined 



of mica and quartz with plumbago, and perhaps a little 

 aluminous matter; so that upon the whole, I must for the 

 present call this rock Dlumbasrinous mica slate. 



