GEOLOGY OF THE WHITE MOUNTAIN DISTRICT. 99 



plane is coincident with that of the strata. On the contrary, there is 

 often no arrangement to correspond with the stratification. Owing to 

 scanty exposures, and to the abundant accumulations of decayed rock, 

 earth, and vegetable mould, it is often difficult to determine to which of 

 the two varieties of arrangement referred to above each example belongs. 

 It is obvious that one of these rocks must be a granite, and the other 

 gneiss. In our explorations no distinction has been made between them. 

 The assumption has been that the agencies producing the granite oper- 

 ated with greater intensity, so as to induce a pasty condition in the mass, 

 and obliterate the stratification without destroying the porphyritic aspect 

 of the rock. If the difference in condition involves radical distinctions 

 in the mode of origin or in the time of the fusion, then there are two 

 formations to be considered instead of one. But in that event the sec- 

 ond rock was derived from the first, so that the assignment of both to 

 one group at present will not lead to error in respect to the geographical 

 areas occupied by the porphyritic rock. 



The mica in this rock is supposed to be muscovite. It is usually black, 

 or of a very dark brown color. Quartz is scarce, varying with the local- 

 ity, and it is always amorjahous. Iron is so abundant that most of the 

 exposures are stained by its oxidation. The texture of the rock is rather 

 coarse, the crystalline particles averaging from one sixteenth to one 

 eighth of an inch in length. 



This formation is disposed along two converging lines in the White 

 Mountain district. The first extends from about the line of Carroll and 

 Franconia along the westerly base of the Franconia mountains into Ben- 

 ton, spreading out broadly in Lincoln and Woodstock east of Moosilauke, 

 and sending a spur from Bald mountain in Franconia into the valley of 

 the Pemigewasset, certainly as far as Walker's falls. This is the main 

 range, and it seems to terminate in Campton and Rumney. The second 

 area extends northerly from Ashland and Holderness to Waterville, being 

 a part of a range largely developed in the Merrimack district. Beyond 

 Waterville it may be said to bifurcate, part appearing in the valley of 

 Sawyer's river in Elkins's grant, and part taking an easterly course 

 beneath Mt. Whiteface into Conway. 



The tvestcrn range. Plate VI, Fig. 7, shows the relations of the west- 

 ern range of this rock in Franconia to the adjacent formations, as well as 



