240 STRATIGRAPHICAL GEOLOGY. 



to the same class of porphyritic breccia with that upon Mts. Mote and 

 Pequawket. From the crossing of the axis of the ridge by Little river, 

 to a short distance south of the north Twin mountain, the granite is 

 specked by small black pieces of mica or hornblende schist, and quartz 

 crystals are abundantly disseminated through the feldspathic paste; and 

 jointed planes dip about ten degrees northerly. The north-west spur, or 

 the mountain mass west of the small stream flowing northerly from the 

 summit, is of the Albany variety. The south Twin mountain has been 

 mentioned as being composed of porphyry. The length of this mass 

 holding black fragments of schist is a little over two miles. 



Mts. Willard and Tom. 



On page 177 allusion is made to the presence of a narrow band of 

 breccia on the south face of Mt, Willard, and on page 165 to the same 

 upon Mt. Tom. On page 178 it is remarked that masses of the same 

 slate breccia occur just behind the north spur of Mt. Field. All these 

 cases I conceive to be examples of the same breccia occurring so abun- 

 dantly upon Mts. Pequawket and Mote, though none of the masses found 

 are known certainly to exceed twenty feet in thickness. They all occur, 

 also, on the eastern border of the slate adjacent to the Albany granite. 

 They are of too limited extent to be represented upon the general geo- 

 logical map. 



A large portion of the Mt. Willard breccia differs from that on Pe- 

 quawket in being much more compact, in containing a variety of pebbles, 

 and in having a different cementing material. The rock superficially 

 resembles trap with a glazed coating or tarnish in the joints, and fre- 

 quently no fragments are displayed, except after weathering. The mate- 

 rials are principally a compact slate, a looser schist, with pretty black 

 mica (phlogopitc?) sprinkled through it, gneiss, granite from veins in the 

 Montalban series, and numerous very small bits of glassy quartz not crys- 

 talline. The paste is dark gray, considerably lighter than the schistose 

 fragments, and is notable for the very black scales of mica (muscovitei*) 

 scattered through it. Some irregular patches of white feldspar may be 

 connected with the paste rather than with the fragments. This breccia, 

 though quite near the Franconia group topographically, is very distinct 

 from it in the character of the paste and the included fragments. The 



