GEOLOGY OF THE WHITE MOUNTAIN DISTRICT, 2\^ 



Labradorite Area north of Tripyramid. 



Mr. Huntington discovered fine exposures of labradorite and the re- 

 lated formations in ascending that tributary of Swift river called Sabba 

 Day brook. Near the mouth of the stream there is a cataract falling 

 over Conway granite, which is the common rock of the country. The 

 same appears a mile higher up. It also occurs on Downs's brook, another 

 tributary of Swift river, running very nearly along the line between Water- 

 ville and Albany. The Albany granite was not observed here, possibly 

 because we had not learned the importance of distinguishing it at the 

 time of the visit. But higher up Sabba Day brook Mr. Huntington found 

 compact labradorite in place, apparently devoid of chrysolite, and frag- 

 ments whose cleavable crystals displayed the play of colors usually seen 

 in this species. Higher up the mountain (the north Tripyramid) the 

 sienitic rocks of the slide reappear in the same order as in the ascent of 

 Norway brook, apparently cutting the labradorites. Farther south the 

 labradorite passes into a breccia apparently overlying gneiss. It is proba- 

 ble that the Albany granite joins the labradorite on the north, since speci- 

 mens apparently referable to it came from the Flume brook, about two 

 miles to the north of Tripyramid. The small area of gneiss south-east 

 has been mentioned upon pages 131 and 133. Otherwise, most of the 

 rocks on the east belong to the Conway granite series. On the south 

 and south-west this Labrador area is flanked by porphyritic gneiss. Fig. 

 19 will show the position of the ossipytes, compact lime-felsites, and the 

 sienites between Beckytown and Swift river, passing over Tripyramid, 

 and their supposed relations to the adjacent porphyritic gneiss and Pemi- 

 gewasset granites. 



Labrador Area upon Mt. Washington River. 



Upon pages 125-127 the Montalban rocks upon the Mt. Washington 

 river are spoken of in connection with labradorite. This is an important 

 locality, as it shows the relations between the Montalban and Labrador 

 systems. The details of the former series have been already given, with 

 as much precision as possible. The latter area extends only about a mile 

 along the river. Its width is not ascertained ; but G. N. Merrill, of Jack- 

 son, assures me he has seen this rock on a tributary stream midway 



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