1870.] HUNT — ON NORITE OR LABRADORITE ROCK. 33 



ordinary Laurentian gneiss. Bayfield, moreover, describes a rock 

 with a base of labradorite as forming the coast for several miles 

 toward Mingan. Finally, it is widely spread on the coast of 

 Labrador, where its characteristic mineral was first found, and 

 from whence it takes its name. 



Prof. A. S. Packard, Jr., has given us valuable information 

 with regard to the occurrence of labradorite rocks at some points 

 on the Labrador coast. ^ One of its localities is at Square Island, 

 just north of Cape St. Michel, were the rock consists chiefly of 

 crystalline labradorite, smoky-gray in color, translucent, and 

 opalescent, with greenish reflections. This feldspar often shows 

 'cleavage planes two inches broad, and is associated with a little 

 vitreous quartz, and wir.h coarsely crystalline hypersthene, which 

 appears in relief on the weathered surfaces. This labradorite 

 rock, according to Prof. Packard, is surrounded by and probably 

 rests upon Laurentian gneiss. At Domino Harbor he found 

 domes or bosses of a similar labradorite resting upon strata which 

 consist in great part of a slightly schistose quartzite, having for 

 its base a granular vitreous quartz, and enclosing grains of black 

 hornblende, or more rarely hypersthene, black mica, and red 

 garnet. Feldspar is generally wanting, but in some parts these 

 quartzites become gneissic, and they where nowhere seen in un- 

 comfortable contact with the Laurentian gneiss of the vicinity. 

 These quartzose strata Prof. Packard refers, with some doubt, to 

 the Huronian system. The minerals which they contain are not, 

 however, met with, so far as known, in the Huronian quartzites ; 

 and, on the contrary, are very characteristic of the quartzites of 

 the Laurentian system, which attain a great thickness in many 

 parts of its distribution. The overlying domes of labradorite 

 rock, which Prof. Packard was inclined to regard, in this case, as 

 erupted through Huronian quartzites, are probably nothing more 

 than outlying portions of the newer Labrador formation resting 

 upon the Laurentian strata, as already observed by him at Square 

 Island. Along the western coast of the island of Newfoundland 

 Mr. Jukes observed, at Indian Head and at York Harbor, dark 

 colored rocks composed of labradorite and hypersthene and others 

 on albite (?) and hypersthene, which may probably be found to 

 belong to the Labrador series. 



* On the Glacial Phenomena of Labrador and Maine. Mem. Bost. 

 Acad. jSTat. Hist., vol. I., part ii., pp. 214-217. 



Vol. Y. C i^o. 1 



