THE TEERESTillAL PERIDOTITES. — LHERZOLITE. 139 



Sec. 29, T. 48, R. 27. Three and one-half miles nortlwest of Ishpeming, 



Mtchiijan. 



242. A gray, somewhat fibrous rock. Section: a gray mass traA'ersed by a networlc 

 of magnetite. It is composed of a liglit gray and colorless transparent mass of serpentine 

 with some dolomite, and has the usual reticulated arrangement of the magnetite so char- 

 acteristic of the serpentines produced from the alteration of olivine rocks. 



241, from the same locality, is a greenish- and reddish-brown rock traversed by green- 

 ish-gray serpentine veins. Weathers light yellowish-green. The reddish-brown color is 

 owing apparently to a ferruginous staining of the serpentine folite. Section is brownish- 

 gray and conqjosed of a pale greenisli-yellow serpentine traversed by irregular reticulated 

 magnetite bands, and spotted by in-egular ferruginous stains of reddisli- and brownisli-yellow. 

 While in the hand specimen these stains present the appearance of distinct micaceous 

 folia?, I am unable by the microscope, either in conmion or polarized light, to find any 

 structure peculiar to them and distinct from tlie serpentine, beyond that belonging to 

 ordinary ferruginous stains. The serpentine shows an irregular fibrous and lamellar 

 structure in polarized and common liglit. 



245, from the same locality, is similar to the preceding. Its staining is deeper, and 

 the rock is coated on one side with a chrysotile and dolomite vein. In the section tiie 

 fibrous structure, tlie magnetite network, and the ferruginous staining are all more 

 strongly marked than in the preceding. 



243, from the same locality, is a greenish-gray rock with the ferruginous staining 

 showing in a few spots only, — principally along fissures. The section is gray, and under 

 the microscope is seen to be composed of pale greenish-yellow serpentine with cloudy 

 spots. These appear to be occasioned by a fine magnetite dust, which is generally associ- 

 ated with an approach to crystallization on the part of the surrounding material, M'hich 

 somewhat affects polarized light. Numerous pale greenish scales occur in abundance in 

 the serpentine, and have the polarization characters of talc. Crystals and grains of mag- 

 netite are scattered throughout the section. 



235, from the same locality, is a clear translucent green serpentine containing magne- 

 tite grains. It weathers light-colored, even to a chalky-white. The section forms a clear 

 almost colorless mass spotted with ciystals and grains of magnetite. The same mineral 

 also traverses the section in the form of a vein. In common light the clear serpentine 

 mass shows fibrous structure, which is beautifully brought out in polarized light. The 

 magnetite appears as a secondary product. 



Associated with these are other sjiecimens of greenish- and reddish-brown serpentine 

 often traversed by dolomite veins. In large masses this dolomitic material with talc 

 seems to have replaced nearly all of the serpentine, giving rise to a rock called locally 

 limestone. Much chrysotile also occurs.* 



Transylvania, Austria. 



Tschermak describes a schillerfels f from this region as a dark-green rock with white 

 spots composed of olivine, bronzite, diallage, magnetite or chromite, and a little anorthite. 



* See further. Bull. Mus. Comp. Zool., 1880, vii. G5, 66 ; Wright, Mineral Statistics of Michigan, 1879, 

 pp. 201-l'06; Romingcr, Geo!. Michigan, 1881, iv. 137-113. 



t Hcrbich appears to class this with eruptive rocks. Verh. ilittli. Natiir, Herinannstadt, 1865, xvi. 

 172-1S3. 



