Portland and its Vicinity. 317 



tinues nearly four miles. I have met with it in other 

 places around Portland; but nowhere occupying extent 

 of surface enough to be exhibited on the map. Nor am 

 I sure that I ought to have extended the stratum of this 

 rock on Cape Ehzabeth to the ocean southwesterly, as I 

 have not actually traced it so far. But the remarkable 

 uniformity in the dip and direction of the rocks around 

 Portland, has led me in some instances to extend them 

 on the map, somewhat beyond where I have actually 

 traced them on thfe surface. 



In passing along the coast from Portsmouth, New 

 Hampshire, to the mouth of Casco river, we find numer- 

 ous ranges of hornblende slate, separated by other rocks, 

 particularly greenstone and sienlte. Between Portsmouth 

 and the east part of York, we meet with greenstone only, 

 as the alternating rock ; and I am inclined to believe (my 

 opportunities for observation have been very limited,) that 

 it is the primary greenstone; and consec^uently, Is only a 

 variety of the hornblende slate, which has lost, more or 

 less, its slaty and stratified structure. But between the 

 east part of York and Casco, we meet with ledges of 

 decided sienite, resembling that on Cape Ann. At Bid- 

 deford; on the west bank of Casco river, vast ledges of 

 this rock appear, and are quarried. In that rock I could 

 not discern any hornblende ; but it is nearly destitute of 

 mica, and corresponds to a great deal of the rock in Mas- 

 sachusetts called sienite. 



From Portsmouth to Casco the general direction of 

 the stratified rocks is northwest and southeast, and the 

 dip northeasterly and large. But from Casco to Port- 

 land, the mica and talcose slates (perhaps I ought to add 

 also the argillaceous slate,) run northeast and southwest, 

 and dip northwest, from 70^ to 80^. Casco river, then, 



