THE IGNEOUS ROCKS. 511 



are probably likewise altered diabases. The alteration in the two cases is 

 somewhat diiTerent, since in the talcose-schists all of the original iron, which 

 in the case of the chlorite-schists was largely retained in the chlorite, has 

 been lost. The talcose-schist dikes are confined niainlv to the vicinity of 

 the ore deposits in the soft-ore mines, while the chlorite-schists are less 

 common here than they are in the hard-ore mines, although they are prac- 

 tically universal in their distribution. Evidently the talcose-schists may be 

 looked upon as chlorite-schists from which the iron has been leached by 

 the same process that secreted the ore bodies in their neighborhood. 



The "paint-rocks" require but little special mention. The ocherous 

 coloring matter coats the talc fibers and the grains of the other components 

 in the schists, into which it has evidently been introduced since the rocks 

 were transformed into schists. In a few of the "paint-rocks" the coloring 

 matter is magnetite or martite rather than ocher or limonite. The oxide in 

 these rocks occurs as little octahecba embedded in the talc and (juartz. 

 It was introduced after the schist became foliated, for its grains are scat- 

 tered tlirough the rock mass without respect to its foliation, and, so far as 

 has been noticed, they have produced no efl^ect upon the disposition of the 

 talc fibers in their vicinity. There is no bending of the fibers around 

 the larger crystals, as would be the case were these present when the rock 

 became foliated, but they are cut off abruptly by the opaque iron oxide, 

 as though they passed directly through its crystals. Although the greater 

 portion of the magnetite and martite crystals are opaque, on their borders 

 they are often changed to hematite, and little plates of this substance also 

 occur as elongated lenses in the body of the rock. These latter plates 

 appear to be altered forms of a preexisting magnetite. They probably 

 represent little grains of this substance that were present in the original 

 diabase. 



There are a few other light-colored schistose rocks that are some- 

 times met with as dikes cutting the iron-bearing formation. They are not 

 usually distinguishable from the talcose-schists in the hand specimen, 

 and so they have generally been confused with the latter rocks, and have 

 been called by the same names as these, viz, soapstones when light- 

 colored, and "paint-rock" when stained. Under the microscope the fibrous 



