AOID INTKUSIVES. 197 



tlirough the sedimentary rocks which now surround it the g-ranite included 

 fragments of them. 



In addition to this a well-defined banding is still present in these frag- 

 ments. Though by no means conclusive evidence, this is considered as an 

 indication of their having been originally deposited through the mediation 

 of water. The sediments have been completely recrystallized into fine- 

 grained mica-gneisses. 



The sedimentary fragments included in the granite now show the 

 following characters. They are composed of layers of two kinds. The 

 one kind of layer is very fine grained, of gray color, and consists predomi- 

 nantly of biotite in fairly good automorphic plates, muscovite in small 

 quantity — but in automorphic plates — even with respect to the biotite, 

 feldspar, quartz, and iron oxide. The feldspar is in small equidimensional 

 grains. Onl}" one finely striated feldspar was observed, the greater part 

 possibly being orthoclase. It shows in places a well-developed zonal 

 structure, the zones conforming to the outlines of the grains. The zonal 

 structure probably depends upon varying quantities of the soda and jDotash 

 molecule. Quartz occurs in grains in very small quantity. 



The second kind of layer which is seen in the fragments is much coarser 

 grained than is the first, just described, and is very much darker. It is 

 composed mainly of muscovite and biotite, in about equal quantities, feld- 

 spar, quartz, magnetite, and ilmenite, with some tourmaline. Both feldspar 

 and quartz occur in grains, the former in small quantity. The biotite is in 

 small plates less well developed than the muscovite, though mostly auto- 

 morphic. It is partly bleached and has associated with it here and there 

 some secondar}" epidote. The muscovite is in very large automorphic 

 plates, some of them twinned according to Tschermak's law, and includes 

 flakes of biotite and grains of quartz and feldspar. This gneiss contains 

 also a large number of crystals of tourmaline, showing strong dichroism 

 from light pinkish to dark grayish blue. Iron oxide is present, both as 

 magnetite and as ilmenite. The quadratic individuals of the one and the 

 hexagonal plates of the other at times are very well developed. No signs 

 of pressure whatsoever are seen. 



The muscovites evidently represent rhe last product of crystallization, 

 as shown by their including all the minerals which had been previously 

 formed. (Fig. A, PL XXXIV.) These muscovites are probably to be 



