. Annals of the New York Academy of Sciences. Science; Science -- New York (State). ROGERS, GEOLOGY OF THE CORTLANDT SERIES 71 green), giving the mineral a curious washed-out appearance. The analysis shows it to contain per cent, of FeO, so that it is bronzite. It may become very abundant, so that the rock is almost a bronzitite, which was never noticed in the typical norite proper; and magnetite, moreover, is almost lacking. The writer has three slides containing the contact of this rock with spinel emery. In every case, the feldspar is continuous over the line; in two the spinel and mag
. Annals of the New York Academy of Sciences. Science; Science -- New York (State). ROGERS, GEOLOGY OF THE CORTLANDT SERIES 71 green), giving the mineral a curious washed-out appearance. The analysis shows it to contain per cent, of FeO, so that it is bronzite. It may become very abundant, so that the rock is almost a bronzitite, which was never noticed in the typical norite proper; and magnetite, moreover, is almost lacking. The writer has three slides containing the contact of this rock with spinel emery. In every case, the feldspar is continuous over the line; in two the spinel and magnetite are sharply segregated from the norite, while in the other the minerals mingle for the space of about 1 mm. The feldspar of the emery is somewhat serictized, and its amount is surprising, considering the black heavy aspect of the ore. In one of the slides, a line of spinels diverged from the main mass and ran out over the norite, crossing the bronzites indiscriminately. Sillimanite Schist Sillimanite schist is usually light gray in the specimen and of a fine,, somewhat fibrous texture. The blades of sillimanite, however, can gen- erally be distinguished, and they sometimes reach one half an inch in Cord,.,-*. ^^ lfe*^Sl,!,mBni*r length, or rarely an inch or more. This rock is extremely tough and so hard that it will turn a drill at times. The "ore" from the Dalton property and from the latest cutting of the McCoy mine is largely this rock, al- though it is a poor abrasive, powder- ing when Under the mi- croscope in typical cases, it is seen to be made up chiefly of sillimanite. This is largely fibrolite, with the blades scattered more or less abun- Fig. 5. Sillimanite Schist. SI. 304 dantly through it. These latter are blotched with a fine brown dust in places, and they also carry abundant magnetite inclusions. Cordierite is almost always present in varying amount; its biaxial figure and the strongly pleochroic yellow halos which surround its inclusio
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectscience, bookyear1879
