144 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



prismatic zone. Delicate needles of briglit-red rutile penetrate this crust 

 or rest upon it. Broad, warped sheets of menaccanite also are implanted in 

 or planted upon the corundophilite, while epidote, margarite, and diaspore, 

 though generally somewhat intermingled with the chloritic basal layer, 

 find their principal development later. The epidote, which is rare, fills 

 cavities with an open network of yellowish-green needles. The diaspore, 

 in the limited portion of the vein in which it was found, sometimes filled 

 fissures 50-G0°"" across with a mass of pink blades irregularly arranged. 



The margarite, while it sometimes rests on and in the chloritic layer, 

 with its base parallel to the surface, more commonly arranges itself in com- 

 pact masses of broad plates at right angles to the surface of the joint plane, 

 and rests on the chlorite, and two such sheets often meet in the center of the 

 fissure with a central sutm-e, and this fills the whole cavity. The "fringe 

 rock," generally a compact corundophilite with abundant radiating hexagonal 

 prisms of brown-black tourmaline, belongs to this second stage. 



Calcite is sometimes found between the diaspore and the corundoph- 

 ilite, though its most abundant development occurs later, and menaccanite 

 occm-s also in the central suture, between the seams of margarite, in much 

 curved laminae. Chalcopyrite is noted by Professor Shepard in margarite, 

 and brookite embedded in diaspore. Parallel with this second stage in its 

 earlier portion, or perhaps even earlier, may be placed the rare secondary 

 veins of grayish-white corundum, which reach a thickness in the magnetite 

 of 1.5-20™^ and show single cleavage faces across the whole width of the 

 vein. I have not found these so associated with other minerals as to exactly 

 fix their age. Other veins in the compact magnetite, 5-10°"° wide, appear 

 at first sight to be almost entirely calcite, but on dissolving this away the 

 following paragenesis appears: 



(1) Corundophilite resting on the magnetite, 1-4°'" wide, in tapering 

 hexagonal crystals, mingled with (2) rutile in its upper portion. The rutile 

 in long, hair-brown, shining, striated needles, often bent and twisted, often 

 sagenite-like, in groups of deeply grooved needles. This is followed by (3) 

 a layer of corundum, partly colorless, partly a most beautiful sapphire-blue 

 or pale pink, crystallized in flat plates, which are very acute rhombohedra, 

 with one pair of faces developed greatly in excess of the others, as is 

 indicated by the fact that, laid on the broadest face, the ring system appears, 

 with convergent polarized light, very eccentrically placed. This layer 



