2l6 STRATIGRAPHICAL GEOLOGY. 



hornblende, with less mica, and the rock is of a reddish cast. Specimens 

 precisely like these came from the north peak of Tripyramid. On the 

 north slope of this peak there is a recurrence of the more grayish variety 

 found between the Notch and the Elbow. In this a black mica excludes 

 most of the hornblende. Near the head of Sabba Day brook the coarser 

 white aggregate containing epidote, etc., is found again, though our speci- 

 mens do not indicate the presence of that particular mineral. On the 

 ridge north of the north pyramid are gray sienites with labradorite, re- 

 sembling those immediately adjacent to the ossipyte on Norway brook. 

 The rocks from the west side of the ridge east of Tripyramid correspond 

 better with the coarser white rock of the Notch. From this inspection 

 of specimens, taken from almost a section line up Norway brook to North 

 Tripyramid, and thence to the labradorites on Sabba Day brook, it ap- 

 pears that the different varieties of this sienitic rock correspond well with 

 each other, very much as if the mountain were a synclinal axis, consist- 

 ing of four leading varieties of strata, with only slight inclinations. The 

 contact of the ossipyte with the sicnite seems to show clearly the cutting 

 of the former by the latter, while this stratiform arrangement of the dif- 

 ferent varieties of sienite is analogous to the mutual relations of the Con- 

 way, Albany, and Chocorua granites. Until further advices, this sienite 

 must therefore be regarded as an eruptive rock. 



There is but one other New Hampshire locality known where a similar 

 rock appears. That is in the adit of the Jackson tin mine. I am not 

 sure that the ledge crops out at the surface; but the fragments brought 

 out by excavation reveal an abundance of sienite, which cuts the schists, 

 in company with the Albany granite. The principal part of the rock is 

 a coarsely crystalline labradorite, with considerable hornblende and ortho- 

 clase crystals in small amount. Quartz is scarce, as at Tripyramid. Mr. 

 Huntington states that Mt. Pleasant, in Maine, one of the outlying peaks 

 of the White Mountains, carries the same rocks as Tripyramid. The 

 area of Pleasant is about the same with that of Tripyramid, and it is given 

 on our general geological map. 



While the sienite is of later age than the Labrador formation, we can- 

 not yet ally it with the sienites of Gunstock and Exeter. Its nearest 

 analogue is the sienite of Frankenstein cliff and Mt. Whiteface, which 

 are for the present placed with the Chocorua granite. 



