GEOLOGY OF THE WHITE MOUNTAIN DISTRICT. 1 43 



is not needed to determine the particular mineral species present. The 

 feldspar is mainly a flesh-colored orthoclase, but oligoclase is common in 

 Franconia and Conwa}^ and probably universally. I have also observed 

 that the quartz is rouij;hly crystalline, whenever carefully examined. The 

 mica is thought to be an ordinary dark muscovite. There are many 

 subordinate varieties connected with this mass, v>^hich will be noticed at 

 the proper time; but the typical rock known as the "Conway" is the 

 best example of a real granite found in the state. 



The Albany granite was first brought to notice at the same time with 

 the other, in 1871, but received the designation of "trachytic," in allusion 

 to a slight resemblance to the volcanic product known as trachyte. It is 

 porphyritic in structure, having crystals of orthoclase imbedded in a fine 

 granitic paste. Two prominent varieties should be noticed, — the one 

 carrying bits of quartz, the other entirely devoid of it; and in this latter 

 case containing the mica disseminated through it, looking as if the rock 

 had been sprinkled over with pepper. The latter variety is the more 

 abundant of the two. A small per cent, of manganese is often present. 

 The porphyritic crystals from Albany gave to Prof. Seely, of silica, 61.6; 

 of alumina, 22.2 ; of lime, .8. The other percentages were not determined. 



In regard to the distribution of these granites, it may be said in gen- 

 eral that they occupy the area bounded northerly by the Ammonoosuc 

 as far as the Crawford house, then easterly by Mt. Webster, from whence 

 the northerly boundary passes easterly to Chatham. From Chatham the 

 line passes east of Mt. Pequawket, and takes in the Green hills of Con- 

 way. The Hne then curves westerly from the south part of Conway to 

 Waterville, whence it passes north-westerly and northerly to the Basin 

 in Franconia, and above the Lake of the Clouds on Mt. Lafayette. From 

 thence the boundary is somewhat east of north till the Ammonoosuc 

 river is reached near the Twin Mountain house. In proceeding to a de- 

 tailed description of the occurrence of these rocks, I will follow the order 

 just indicated. 



Passing southerly from the Twin Mountain house, by way of the three 

 "Sugar Loaves," we find, first, the ordinary coarse Conway granite. On 

 top of the first two peaks the rock holds more than the ordinary quantity 

 of black mica. Between them there is an unusual proportion of quartz 

 present. In the saddle between the second and third peaks the planes 



