BIOTITE MUSCOVITE-GRANITE. 315 



this distance tlie exact contact is covered, but the rocks can be studied at 

 points a few feet from it, and the change from the oue rock to the other 

 seems to be quite abrupt. 



From this boundary it extends westward to the Mill River, and it is 

 abundantly exposed along the road beside the river from Leeds to Williams- 

 burg. As already indicated, it is found to be more and more replaced by 

 dikes of pegmatite as one goes out to the border of the area and up to the 

 higher levels. 



It makes always the impression that it was the original rock, and that 

 the pegmatite was injected into it at a later time, perhaps only slightly 

 later. Around the periphery of the area its dikes are very abundant in 

 Groshen and Chesterfield, and less so in Conway and Blandford. Its dikes 

 are so uniformly interbedded in the schist around the Goshen anticline 

 that I for a long time mapped it as gneiss, until at the south end of South 

 street in Chesterfield, near C. Damon's, I found it cutting across the beds 

 of the schist. In these dikes it is of a little finer grain and more friable 

 than in the main stocks. 



PETEOGEAPHICA.L DESCRIPTION. 



In the middle quarry west of Moore's and east of Florence it is 

 medium-grained, very fresh biotite-granite, with little muscovite, very 

 feldspathic, and showing abundant triclinic striation. The quartz is rare 

 and occurs in rounded grains, as if resorbed. It contains fluid cavities in 

 enormous quantity, of grotesque forms and in lai'ge sheets, often with 

 bubbles, some moving rapidly, some slowly, and some being stationary. 

 They contain water and carbon dioxide. Large, rigid needles of rutile also 

 occur. The feldspar, mostly triclinic, is centrally decomposed into a brown, 

 opaque mass of kaolin scales. The naiTow, fresh border seems almost as 

 if it were a secondary growth. Extinction, 18° on either side. Orthoclase 

 and microcline are also present, but in small quantity, and the large amount 

 of plagioclase allies it to the toualite. 



OHEMICAl, ANALYSIS. 



Analysis I, following, was made by Mr. L. G. Eakins from a speci- 

 men of the best quarry stone of coarser grain from Moore's quan-y, Flor- 

 ence, from which also the slides were cut. It is remarkable Iioav exactly 

 this analvsis agrees with that of the lighter varietv of the jMousou gneiss, 



