228 STRATIGRAPHICAL GEOLOGY. 



7. The Pilot Range. 



This has been spoken of heretofore (p. 70, ct scq.). The principal area 

 occupies parts of Northumberland, Stark, Kilkenny, and Jefferson, twelve 

 miles in length, and is coterminous with remote mountains rarely visited, 

 save Mt. Starr King, near the Waumbek house in Jefferson. There are 

 two smaller areas, scarcely disconnected from the main mass, in Nor- 

 thumberland. On the south side of Mill mountain, in Stark, vertical 

 strata of arenaceous schist abut against the porphyry, with a strike nearly 

 at right angles to the course of the former. At first, I supposed this in- 

 dicated an elevation of the schists by the side of an older, harder mass. 

 A recent visit to outcrops east of A. Sawyer's in Northumberland would 

 seem to indicate the protrusion of the porphyry through fissures in the 

 schists, and hence the later origin of the former. If this be the correct 

 view, it follows that the whole Pilot Mountain area is an overflow of 

 igneous rock, resting upon the upturned edges of Huronian schists and 

 Atlantic gneisses. That is the view presented in the fuller account of 

 this region, already referred to. 



SIENITE. 



The principal sienitic area in the White Mountains has been spoken of 

 in connection with the labradorite rocks of Waterville (Fig. 19). It was 

 described in connection with those rocks for the sake of sketching its 

 relations to them. Moreover, the composition of that mineral aggregate 

 is peculiar, containing triclinic feldspars. The specimens from other lo- 

 calities differ in that respect, no feldspars having yet been detected in 

 them, except orthoclase. None of them, — neither that with the triclinic 

 feldspars nor the Chocorua varieties, — seem to agree exactly with those 

 in the other districts of the strata, unless it be a few about Lake Umba- 

 gog and Island Pond, Vt., in the Coos and Essex region. 



We have noticed sienite at Jackson, Frankenstein cliff, Mt. Whiteface, 

 Mt. Passaconnaway, several places in Albany, and boulders, from some 

 unknown locality, near the Crawford house and Mt. Washington river, 

 besides that of Mt. Tripyramid and the Jackson tin mine. 



In cHmbing Mt. Whiteface, the lower portion, so far as known, consists 

 of porphyritic gneiss, and the balance, perhaps a thousand feet, is made 



