316 Sketch of the Geology of 



, slaty, by removing the diluvium farther from the shore. 

 A quarry of good marble so near, would certainly be of 

 some importance to the city of Portland. How far the 

 stratum extends in a southwesterly direction I am not 

 able to say ; not improbably to the ocean : but the coun- 

 try is somewhat level, and the rocks not often visible. 

 On the map, I have represented this- stratum as quite 

 narrow, and only a few miles long. Not improbably it 

 may be found to extend northeasterly to some of the 

 islands in the harbor. The dip and direction of its layers 

 correspond to those of the slates already described, viz. 

 running nearly northeast and southwest, and dipping 

 almost ninety degrees. 



i 



Hornblende Slate. 



This Is one of the most uninviting and perplexing 

 rocks with which the geologist meets. Where it exists 

 in its greatest purity, that is, where it is distinctly slaty 

 and highly crystalline, its appearance is attractive. But 

 for the most part, it seems to be in a metamorphic state ; 

 its slaty and stratified structure being very obscure ; the 

 rock breaking into fragments, either amorphous or some- 

 what columnar; its crystalline structure becoming less 

 distinct, and constituting m fact, the rock that used to go 

 by the name of primary greenstone. This description 



characters 



form 



acterized as to be mistaken for other rocks, with which it 

 is often confusedly interstratified. In passing from Port- 

 land to the light houses on the extremity of Cape Eliza- 

 beth, we meet with this rock half a mile beyond the new 



part 



f 



