124 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



the talcose slate occurs, having an average thickness of 20 feet on the South Mountain 

 and widening out on the North Mountain to a breadth of nearly 200 feet as it reaches 

 the terminus of the vein in the bed of the Westfield River. 



The gneiss, more especially in the vicinity of the vein, is a very peculiar rock. 

 It abounds in thick seams of a coarse- grained very black and shining hornblende, 

 and where this is not found it is much veined and penetrated by epidote. The 

 stratification is much contorted also, and when the surface of the formation happens 

 to be weathered or water-worn its basseting edges strikingly resemble in color some 

 of the serpentine marbles. It is also noticeable that in it quartz is everywhere 

 singularly deficient. Traces of a white calcareous spar (calcite) are now and then 

 visible upon the joints of the gneiss, with occasional specks of yellow copper, together 

 with malachite stains, but no corundum, emery, or magnetite particles have thus far 

 been detected as constituents of the gneiss itself It is quite otherwise, however, with 

 the talcky rock exterior to the wall of gneiss, for that formation in all its different 

 varieties of talcose slate, soapstone, chloritic aggregates (with included seam of 

 indianite), talcky dolomite, etc., which together constitute the stratum separating the 

 gneiss from the mica-slate, contain here and there disseminated grains of either emery, 

 corundum, or magnetite, but, like the gneiss again, are strikingly free from quartz or 

 uncombined silica in any of its forms. Indeed, this generally abundant substance is 

 altogether wanting, not only in the emery vein, but in the talcose formations consti- 

 tuting its eastern boundary. It makes its appearance, however, in abundance in the 

 mica-slate as soon as the talcose rocks are passed, showing itself not only as the usual 

 constituent of the slate, but in more or less continuous seams from a few inches thick 

 up to above C inches and sometimes a foot in width. Where the seams are thin and 

 discontinuous the included masses thin out at each end before disappearing, the sharp 

 edges being curved in opposite directions so as to form frequent white patches upon 

 the surface of the rock in the shape of the letter S.' 



Corundum and emery (the former consisting of pure alumina and the latter of 

 the same earth in combination with the protoxide of iron), have been found hitherto 

 almost exclusively in carbonate of lime (marble or saccharoidal limestone), from the 

 substance of which as a mediuia or vehicle free from silica they were precipitated in 

 crystals, nodular masses, or veins. Here, however, carbonate of lime is wanting (if we 

 except a partial development of impure dolomite in one place at the top of the South 

 Mountain) ; but a parent rock or menstruum for the formation of corundum and emery 

 is supplied in a talcose slate series equally deficient in free silica, this being a compound 

 which, if coexistent with alumina and protoxide of iron, would seem to be incompatible 

 with the formation of either corundum or emery, inasmuch as under the play of the 

 ordinary chemical affinities, several very different species would be more likely to result.^ 



' It is in the principal veins of this white quartz that very large crystals of ilmenite (washing- 

 tonite) were found at one spot within a mile from the northern end of the vein. 



"An analogous abeyance of quartz characterizes the aluminous group of the sjiinels, the occur- 

 rence of which is much restricted to limestone and talcose slate ; and since alumina is rarely abundant, 

 even in granular limestone and talcose slate, we appear to have an explanation of the genera] scarcity 

 of the corundom and spinel species in the mineral kingdom. 



