THE CHESTER EMERY P,EI). 



125 



To complete this general description of the locality it may not be deemed super- 

 fluous to add the iuterestinj;- geological fact that in two places the surface of the 

 emery vein (near the summit of each mountain), for a distance of several rods in each 

 case, has been deeply grooved and smoothed by glacial action. That the friction pro- 

 ducing this eftect must have been enormous is apparent from the size and depth of the 

 channels, no less than from the initial hardness of the mineral worn away; and that 

 it could not have been the result of running water is demonstrated by recurring to 

 the example of river action in the Westfleld River upon another portion of the same 

 vein, where no such smootliing eftect has been produced; but in place we have merely 

 an eroded, pitted surface from which the coarse crystalline particles of the hard emery 

 are left projecting, precisely as garnet and staurotide are seen on merely weathered 

 faces of mica-slate. 



Passing now from the geological features of the region we enter upon a brief 

 notice of the vein itself and its mineralogical contents. The principal gangue or matrix 

 may be said to be chloritoidal. It can not properly be called chlorite slate or even 

 chloritic trap, inasmuch as the green chloritoidal mineral it contains is considerably 

 removed in character from the species chlorite. This opinion is based not so much 

 upon its wanting the color and argillaceous odor of chlorite as upon the consideration 

 that where crystallized it is found to be harder and heavier than that mineral and 

 ftu'ther differs from it by containing less magnesia and more alumina and protoxide 

 of iron than belong to chlorite. In fact, it is much nearer to corundophilite, a mineral 

 thus named by me from its being the almost constant attendant of corundum. It is 

 not certain, however, that true chlorite is absolutely wanting in the vein, or at least in 

 the contiguous talcose slate, and inasmuch as masonite and ottrelite, varieties of the 

 species chloritoul, are often present, I shall generally speak of the gangue or vein stone 

 as chloritoidal rock. 



MiNEBALS IN THE VEIN. 

 1. Emery. 



Not a little confusion has hitherto prevailed as to the mineralogical and chemical 

 nature of this substance. A common opinion has been that it is a mechanical mixture 

 of corundum and magnetite, while some have imagined it to be a triple compound of 

 alumina and the two oxides of iron. Dr. Jackson, in view of his own analyses of 

 emery, conceives it to be a combination only of alumina and the protoxide of iron.' 



He found — 



Alumina 



Protoxide of iron. 



1. 



60.4 



39.5 



59. 05 

 40.95 



62.3 

 37.7 



' See Am. Jour. Sci., 2d series, Vol. XXXIX, January, 1865. 



