316 



GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



with which variety this rock agrees most closely. I have I'epeated, for 

 comparisou, the analysis of the Monson rock (II) : 



Analyses of granite from Florence and gneiss from Monson. 



SiO... 

 TiO. . 



AL03. 



Fe^G:, 

 FeC 

 MnO. 

 CaO.. 

 MgO. 

 KiO.. 

 Na.O. 



H;0.. 



T.O5.. 



S 



Cu... 



73.27 



.10 



15. 51 



.33 



1. U 



Trace. 



2.74 



.15 



1.66 



4.79 



4.48 

 .12 

 .38 



5.59 



Trace. 

 Trace. 



TOUKMAilNE DENDRITE ON THE SURFACE OF A BLOCK OF GRANITE FROM LEEDS. 



On the surface of a block of the light-gray granite quarried at Leeds 

 is a Uiyer, one-eighth of an inch thick, which differs greatly from the mass 

 of the granite. The latter is a clear, gray gTanite of medium grain whose 

 mica is mostly a jet-black biotite. The thin layer is a slightly coarser 

 muscovite-granite, and over a large surface beautiful dendritic growths of 

 jet-black tourmaline have formed. (PI. VII.) 



It is clear that boracic-acid emanations have passed through a fissure 

 in the newly formed granite, and have promoted at once the formation of 

 tourmaline and the replacement of the biotite of the granite by muscovite. 



THE ATHOL AREA. 



This enters the county onh' in the east portion of Orange, east of the 

 west branch of Tully Brook, and the boundary is continued northward 

 across the west portion of Eoyalston. The granite, from more rapid erosion, 

 forms a steep valley, out of which rise the steep-sided Big Tully and Little 



