28 STRATIGRAPHICAL GEOLOGY. 



Plate II, illustrating the position of the formations described above as constituting 

 Section I, will be found represented upon page 15 of this volume. 



Section II. From Portland, Me., throiigh Mt. WasJiington, to Aber- 

 cro7nby, P. ^. 



This section is 205 miles long. It passes through the highest pinnacle of the White 

 Mountains, intersects the Green Mountain anticlinal axis in Canada, traverses the long 

 plain of Utica slate, near Montreal, and terminates in the Labrador system. 



The first exposures in the islands of Casco bay, off Portland, are of mica schists, 

 quartzites, soapstone, pyritiferous, plumbaginous, and hornblende schists, referred by 

 us to the Huronian.* The prevailing dip is north-westerly ; but a careful examination 

 of the dips, in the neighborhood where the bay does not conceal the outcrops, indicates 

 the existence of at least six folds in this basin. The main synclinal line is situated a 

 short distance to the north-west of Portland. The formation is essentially the same 

 with that traversed by Section I, in the Merrimack or Nashua River valley, save that its 

 lithological characters are more suggestive of Huronian affiliations. 



The relations of this to the adjacent gneiss of Atlantic age are plain, while the dips 

 of the newer group are the steepest. In Deering, where the formations join, they pos- 

 sess the same inclination of sixty degrees south-easterly. The rock of Phippsburg is 

 gneiss, and is probably continued beneath the ocean to connect with the exposures at 

 the Isles of Shoals. Hence there may be an outer vein of gneiss, embracing the Huro- 

 nian schists as closely as the corresponding formation on the north-west side, as exhib- 

 ited in the section. Perhaps the fact of a usually low dip to the gneiss is not well 

 shown. Two suggestions may explain it : first, the rock may have been formed, meta- 

 morphosed, and elevated before the deposition of the Huronian system, and, at the 

 later period of elevation, the slates being more easily moulded, were forced into the 

 steeper inclination ; or, secondly, a portion of the less inclined strata may belong to 

 our later division, called, for convenience, the Rockingham mica schist, which may 

 easily be confounded with the Montalban series. 



Our information respecting the dips of the rocks to the north-west of Portland, in 

 Maine, is very meagre. The whole distance has been hastily traversed. A synclinal 

 axis is revealed just before reaching Sebago lake ; after which only a south-easterly dip 

 appeared as far as the state line. The ledges are greatly concealed by drift all the way. 

 When more carefully studied, inverted dips will probably be found in many places. 

 There would seem to be one important anticlinal between the Maine and White Moun- 

 tain divisions of the Montalban area. 



One of the striking peculiarities of New Hampshire geology next makes its appear- 

 ance, as revealed upon Mt. Pequawket. Three kinds of granite, with limited masses 

 of slate, compose the mountain. The lowest or Conway granite apparently lies hori- 

 zontally upon the upturned edges of the Montalban schists. This outcrop is the edge 



* Proc. Amcr. Ass. Adv. Sci.,\Zj;i, p. 163. 



