Jrom the Tilly Foster Iron Mine. 373 
The filling is occasionally dolomite and brucite together ; and 
rarely splendent crystals of chondrodite occur isolated in the 
tter. 
The crystallization of the chondrodite and of other minerals 
of the bed is now under investigation by Mr. E. S. Dana, and 
nothing therefore need be added he 
the wall-rock of the bed there are occasional small veins 
containing crystals of hornblende and magnetite, and some- 
times plates of biotite. The magnetite of these veins is octa- 
hedral, with even, polished faces, while that of the ore-bed is 
_ The fragments, large and small, down to those an inch or less 
iN size, are generally coated with a white or greenish serpentine, 
which often looks like a varnish over the surface, and again is 
an inch or more thick.* They all feel soapy to the fingers on 
* Mr. Breidenbaugh found for the composition of the white serpentine (this 
Journ., vi, 209) Pe Al,O, 0°86, FeO 2°57, MgO 40-29, CaO 1°35, K,O 
basis Na,O 0-48, H,O 12°52—100°35, giving She convert ratio for the protoxides 
ca and water 3-1: 4°03: 2, that of serpen jas ve eden 
He obtained for the ed SiO, 40-08, Al,O, 14°21, Fe.O, 11°51, MgO 22°03, 
Na,O 0-22, K,0 9-73, H,O 1°69, Fl trace = 99°47; f tuents of the 
ripidolite, SiO, 32°33, Al,O, 14°56, FeO 5-29, MgO 33°74, CaO 1-04, K,0 0°87, 
Am. Jour. Sc1.—Tuirp Serres, Vou. VII, No. 47.—Nov., 1874. 
