344 Pirsson and Washington — Geology of New Hampshire. 



Art. XXXYII. — Contributions to the Geology of New Hamp- 

 shire. I. Geology of the Belknap Mountains / by L. V . 

 Pirsson and H. S. Washington. (With Plate XL)' 



Introductory Note. — Our object in this paper and in one to 

 follow it is to present the results of a study made in the field 

 and in the laboratory of the occurrence and characters of a 

 group of igneous rocks from a locality about which little is 

 known. Our field work was done in two visits to the area and 

 covers a period of between two and three weeks, during which 

 it was traversed and roughly outlined and the highest peaks 

 and ridges ascended. This was sufficient to give a good gen- 

 eral idea of its geology and of the various rock types. In the 

 lack of a suitable base map on a sufficient scale, upon which to 

 make record, more detailed and careful work was not war- 

 ranted and would have enabled us to add little of interest to 

 the general results presented in this paper. The map used 

 and upon which our results are given is taken from that accom- 

 panying* the Hitchcock Survey, referred to later, and which 

 we have modified to some extent. The topography is more or 

 less generalized and in places somewhat inaccurate, but it is 

 the only one showing topography of which we have any knowl- 

 edge and it has served as the basis of several topographic maps 

 since published for the use of tourists which we have also con- 

 sulted. 



Location and Geography. 



The Belknap Mountains form an elevated tract south and 

 west of Lake Winnepesaukee in New Hampshire and lying 

 in the townships of Gilford, Alton and Gilmanton. Although 

 they are sometimes referred to as the " Belknap Range " they 

 do not form a mountain range of the anticlinal type, being the 

 irregular, eroded upper portion of a great intrusion of igneous 

 rock of a generally granitic character. In its greatest length, 

 which is northwest and southeast, the mountain tract extends 

 about eleven miles and its width at the broadest point east and 

 west is about six miles. In shape the mass is triangular, the 

 long side facing the west composed of the main ridge which car- 

 ries the highest summits, while an eastward extension produces 

 the triangular shape. At the eastern end of the triangle there 

 is an extension running southward. On the north and east 

 sides the slopes descend into Lake Winnepesaukee ; on the 

 west and south into a much lower, irregularly hilly country. 

 The drainage on the west is carried off by the Gunstock River, 

 which in its course of about six miles runs due north at the 

 foot of the mountain slopes in a valley cut along the contact 



