192 THE CRYSTAL FALLS IKON-BE ARING DISTRICT. 



original feldspar material is almost entirely replaced by a mass of musco- 

 vite, with some little epidote-zoisite and biotite. The muscovite in these 

 secondary aggregates gives excellent though small rectangular sections, 

 showing its fine cleavage very distinctly. Well-determinable kaolin flakes 

 were not found. 



The mica is well represented by both biotite and muscovite. Both 

 occur in very well developed crystals, the muscovite showing the most pei"- 

 fect development. The biotite has partly altered to chlorite, with a simul- 

 taneous production of rutile, sagenite, and sphene. Between the chlorite 

 laminte one frequently sees lenticular areas of secondary calcite. Quite 

 commonly the sag'enite is found included in these areas. 



In only one specimen was hornblende observed. This was from a 

 granite dike which cut the dolerite. The hornblende is of a noncompact 

 variety, which upon the edges is finely fibrous. It corresponds exactly to 

 that which is found in the adjacent dolerite. 



The contact between the granite and dolerite appears irregular, as 

 though the dolerite had been to some extent broken. As the contact is 

 approached from the granite side the hornblende increases in quantity. It 

 is thought probable that the hornblende in the granite along the contact is 

 secondary after pyroxene, and that this pyroxene was obtained by the 

 inclusion of fragments of the dolerite. 



Accessory minerals are not present in large quantity. 



Iron oxide is not present in great quantity, and when seen it is usually 

 titaniferous, as rutile is found as an alteration product. In one case the 

 hexagonal plates show the presence of ilmenite. Apatite is rare, as a rule, 

 though occurring in some sections in considerable quantity. Zircon is 

 scarce, as are also sphene and rutile. Epidote is rather common. In some 

 cases it is seen in biotite surrounded by a pleochroic halo, and in such cases 

 it is probably original. The secondary minerals, muscovite, biotite, chlorite, 

 epidote, sphene, rutile, and calcite, show their usual characters. Calcite is 

 abundant, and is more or less ferruginous. It is found in rhombohedra and 

 also in irregular masses. In all cases its secondary origin is clear. 



MICROPEGMATITES. 



The micropegmatitic varieties of the biotite-granite show the same 

 variations in color, from reddish to gray and greenish, and in grain from 



