Portland and its Vicinity. 319 



And Since not more than half a mile of land carriac^e 

 intervenes between this spot and Portland, if such a dis- 

 covery should he made, it must prove of great service. 

 A large part of the stone there used for architectural pur- 

 poses is gneiss, brought from Yarmouth^ twelve or fourteen 

 miles distant. 



In general, the gneiss of the region above described is 

 the granite gneiss ; that is, the rock approaches to granite 

 in appearance, the lines of stratification being almost 

 obliterated, and the texture of the rock being very coarse. 

 Indeed, as it appears in the walls, along the road, and 

 occasionally in ledges, it is easily mistaken for coarse 

 granite. But the experienced eye will soon perceive it 

 to be gneiss, almost changed into granite* In Yarmouth 

 it abounds in schorl, and sometimes affords beryl. The 

 form of the crystals of schorl may be described by calling 

 it a three-sided prism with triedral summits, the edges of 



the prism being replaced by two planes, so as in fact to 

 make a nine-sided prism. 



In passing west and northwest from Portland, we find 

 the mica slate bearing rapidly more and more to the 

 northwest ; that is, dipping southeasterly at a less and 



r 



less angle ; so that w^hen we reach the gneiss, it is not 

 more than 30^ to 35®. Proceeding in the same direc- 

 tion, the dip becomes still less, even as low as 20°. This 

 is an important fact ; because it is contrary to what we 

 should expect ; if, as it w^ould seem we must admit, the 

 anticlinal axis of the system of strata around Portland lies 

 * northwest of the city- But it corresponds w^ith what I 

 have observed of the gneiss in other parts of New Eng- 

 land. Indeed, I scarcely know of any of our rocks, not 

 excepting those of the secondary class, w^hose dip is not 

 as great as that of our gneiss in many places ; though 



