1870.] HUNT — ON NORITE OR LABRADORITE ROCK. 35 



macles, and frequently exhibiting the peculiar opalescence which 

 belongs to labradorite. Although rocks composed of labradorite 

 or similar feldspars, with hornblende or pyroxene, occur in various 

 other geological formations, both as indigenous g:reenstones and 

 as erupted masses, they never, so far as ray observation in North 

 America goes, exhibit the peculiar character just described ; 

 namely, that of a granular or granitoid rock composed of nearly 

 pure labradorite or some closely related feldspar, frequently 

 opalescent, and generally of a bluish color, often violet, smoky- 

 blue or lavender-blue. This type of rock seems in North America 

 to characterize the Labrador series. 



It may here be remarked as an interesting fact bearing on the 

 distribution of the Labrador series, that two large boulders of 

 labradorite rock, one of the beautiful dark blue variety, are found 

 on Marblehead Neck, on the coast of Massachusetts.^ It does 

 not seem probable that these masses could have been derived from 

 any of the far-off localities already mentioned, and the fact that 

 the gneiss of eastern Massachusetts is, as I have recently found, 

 in part of Laurentian age, suggests that an outcrop of the Labra. 

 dor series may exist in some locality not far removed. In this 

 connection it maybe added that I have lately found characteristic 

 labradorite and hyperite rocks in southern New Brunswick, a few 

 miles east of St. John, occupying a position between the Lauren- 

 tian and the Huronian or Cambrian rocks, which there make their 

 appearance, accompanied by Lower Silurian strata, to the south 

 of the great carboniferous basin of the region. This interesting 

 locality was recently pointed out to me by Mr. G. F. Matthew of 

 St. John, to whom we are indebted for a great part of our know- 

 ledge of the geology of southern New Brunswick. Chester and 

 Bucks counties, in Pensylvania, and the Wachita Mountains, in 

 Arkansas, are cited in Dana's Mineralogy as localities of labrador- 

 ite, but as I have never examined specimens from the.se places, I 

 am unable to say whether they resemble the characteristic anor- 

 thosites of the Labrador formation already described. 



* Specimens of these rocks, correctly determmed and labelled, are 

 found in the collectious of the Essex Institute at Salem. To these my 

 attention was called at the time of the meeting, in August last, by Prof. 

 C. Hitchcock, after which, in companv with Dr. G. B. Loring and Prof. 

 Packard, I visited the locality at Marblehead iS'eck, and collected farthei 

 specimens of the characteristic labradorite rock. 



