390 



THE AZOIC SYSTEM AND ITS SUBDIVISIONS. 



'' Considered as an isolated case, it is difficult to dctenninc the i)lancs of strati- 

 fication since two prominent sets of jointed planes exist, either of which might 

 be taken for strata. One set dip about 20° northerly, and are the most numer- 

 ous. The other dip about 75° westerly. More definitely, the following are the 

 supposed strata dips seen in ascending ; about 20° to N. 20° W., N. 80° W., 

 N. 34° E., and N. 40° W. The joints have these strikes, N. 22° W., N., 

 and S The evidence is plain that the Labrador system does not include, 



« 



besides the tri clinic feldspars, the porphyries and all the Pemigewasset granites. 

 Hence the statements respecting the nature of the events transpiring in the 

 Labrador period^ — given in the chapter upon the physical history of the 



strata, — pertain to a later epoch We are therefore led to believe that 



the labradorites alone represent the Labrador system, and, as thus limited, it 



has been described There are seven small areas of it, cut by a sort of 



'sienite' containing triclinic feldspars, and therefore supposed to close the 



perio<l The reality of the system is not affected by the removal from 



it of these various porphyries and granites. Their elimination makes the cor- 

 respondence perfect between the New Hampshire and Canadian areas, thus 

 establishing more firmly the existence of the series. Some difference of opinion 

 may exist among geologists as to the relations between the Montalban and 



Lal^rador systems The labradorite rocks, with a very moderate dip, 



rest un conformably upon the greatly upturned edges of tlie Montalban schists, 

 as if there had been large upheavals at the close of the Montalban period, and 



comparatively little disturbance since The facts as interpreted are of 



great consequence, since they fix the geological horizon of the whole Atlantic 

 system, while considerations of a stratigraphical character confirm this impres- 

 sion The discovery of the Labrador system, overlying the most abun- 

 dant and characteristic White Mountain strata, makes it clear that the latter 

 are older than the former, which are confessedly Eozoic." 



In the Final Report on the Geology of New Hamphirc, Vol. IL p. GG7, 

 Prof. Hitchcock remarks as follows : — 



"The Labrador system, if present in New Hampshire, is in very limited 

 amount. Recent investigations make it difiicult to say that the labradoj'ite 

 rooks are not of eruptive character. They have the composition of d(jlerite ; 

 and certain exposures of them upon Mt. Washington are surely injected 

 dykes. Hence great doubt arises whether the larger area of Waterville 

 really represents the Labrador system of Canada.. At all ev(!nts its age is 

 great, for these dykes cut through Montalban strata. This dolerite may be 

 regarded as one of the oldest eruptive rocks in the state, coming to the surface 

 in what was the Labrador age of the world." 



Resuming tbc Picport for 1871, wo find the relative geological posi- 

 tion of the formations to be stated as follows : — 



" The sections given of the common granite, trachytic granite and the noriau 

 series (or at least certain felsites,) seem to determine their relative positions, 



