Pirsson and Washington — Geology of New Hampshire. 445 



matic character and probably contemporaneous with them, as 

 will be shown later. In its deficiency of plagioclase feldspar 

 it is unlike the aplitic lassenose (adamellite) of the border 

 facies of the main mass next described, and this fact, which is. 

 of importance, will be discussed later. 



JBlotitic-grano-lassenose (adamellite aplite). 



As previously mentioned in the geological part of this paper, 

 the Belknap massif of grano-pulaskose shows on nearly all 

 sides a marginal facies of a light-colored granitic rock into 

 which it gradually passes. Examples of this from various 

 parts of the area have been studied and it has been found to have 

 on the whole a pretty constant composition and character. Its- 

 geological occurrence and relationships have been described 

 under the heading of the contact facies of fine-grained granite,, 

 using the latter name as a field term. 



For purposes of analysis, detailed microscopic study and 

 description, a type specimen was selected from the south end 

 of Piper Mountain, where it is exposed in a cliff near the 

 high road running through the notch to Young's Pond. 



Megascopic. — Phanerocrystalline ; fine-grained ; light brown- 

 ish gray ; dominantly quartzo-feldspathic but dotted with 

 minute specks of black biotite and shining white muscovite * 

 of an even granular texture with sugar granular habit and feel ; 

 distinctly gneissoid and with perceptible eutaxitic structure; 

 of an easy fracture and rather friable. 



Microscopic. — Alkalic feldspar, andesine and quartz essential, 

 biotite and muscovite accessory. Essential minerals present 

 in approximately equal amounts. Average size of grain 0*2 mm : 

 occasional individuals much larger but not phenocrystic ; some 

 smaller. Alkalic feldspar, OrAb, equidimensional anhedral. 

 Andesine, Ab 5 An 3 , equidimensional anhedral to subtabular or 

 subprismatic ; albite twinning common, Carlsbad not common, 

 pericline rare. Quartz equidimensional anhedral, often sphe- 

 roidal. Biotite brown with not intense pleochroism, in form 

 tabular to scaly. Muscovite tabular and scaly. 



Mode. — For the determination by Posiwal's method of the 

 relative amounts of minerals making up the rock, 150 measure- 

 ments were made in a distance of 3000 units. The average 

 size of grain was 0*2 mm . Keduced from volumes to percent- 

 ages by weight this gave : 



Quartz ._. 33*50 



Orthoolase 30-80 



Andesine ( Ab 5 An 3 ) 3 1 -04 



Biotite 3-77 



Muscovite _ _ -83 



100-00 



