GEOLOGY OF THE WHITE MOUNTAIN DISTRICT. 21 5 



clase, labradoritc, and mica, with scarcely any hornblende. The line of 

 junction is irregular, averaging the course N. io° E., being sometimes N. 

 yS° W., while the dip of the plane of separation is about 85° westerly. 

 Some of this feldspathic rock has been injected into irregular cavities of 

 the ossipyte. The irregularities of these veins are shown in Fig. 18. 

 The length of the vein there represented is thirty feet, the greatest 

 width being four feet. The general impression is, that the sienite was 

 an eruptive rock, cutting nearly vertically across the ossipyte. 



Perhaps an eighth of a mile above this junction the interesting assem- 

 blage of coarse crystals of whitish labradorite, hornblende, titanic iron, 

 mica, and epidote (see analysis, p. 40, vol. i) occurs at the Notch. These 

 ledges disintegrate very rapidly. Large nodules of the sienitic rock less 

 liable to decomposition are scattered through the mass ; and there are 

 geodic cavities containing orthoclase, albite, quartz, and rarely stilbite. 

 The Notch is produced by the erosion of a ferruginous band, resembling 

 a stratum, and dipping both E. 25° S. and E. 25° N. Above the Notch, as 

 far as the Elbow, there is a recurrence of the finer-grained sienite, contain- 

 ing geodes and feldspathic veins. At the Elbow there is a somewhat dif- 

 ferent mineral combination, extending to the top of the pyramid. Quartz 

 is rare ; but there are two kinds of feldspar. Mica is abundant, and some 

 specimens show hornblende. The same minerals occur in the geodic 

 masses as below, also, actinolite, amethyst, and others yet undetermined. 



A light-colored feldspar, from a reddish-tinted variety of the "sienite," 

 gave to Prof. C. A. Seely, silica, 59.2; alumina, 28.8; iron oxyd, trace; 

 lime, 7.40; soda, 8.54; potash, 0.6. In this case the silica, alumina with 

 iron oxyd, and lime were determined first. Afterwards, the alkalies were 

 determined separately from a different sample of rock. Judging from 

 these results, the feldspar corresponds very well in composition with an- 

 desite. The type-mineral of this species is said, in Daiids Minn-alogy, 

 to come from a "sienite-like rock" in the Andes. Some analyses of ande- 

 sites from Chateau Richer in Canada, by Dr. Hunt, agree well with this. 

 The red feldspar associated with the andesite in this rock gave to Prof. 

 Seely, silica, 57.6; alumina and iron oxyd, 24.6; lime, 3.2. It seems, 

 therefore, to be related to the same species rather than to orthoclase, 

 but it is not well defined. 



Towards the top of the slide and the mountain there is considerable 



