176 BULLETIN OF THE 



in Figure 8 with black inclusions of magnetite and clear ones of quartz 

 and muscovite, and having the typical irregular flattened shape. The 

 feldspars of this type have a low even polarization tint, yellow of the 

 lower order even in thicker slides, where other feldspars show red and 

 blue. Often without twinning, or else twinned in single halves, less fre- 

 quently multiple twinned with few lamellae, they have the characters 

 of the albite of the schists. Some of these areas of glassy feldspar with 

 the same generp,l characters show the double twinning of microcline. 



A variety of these feldspars is seen in Figure 7, which, having the 

 same flattened irregular shape, with inclusions of muscovite, quartz, etc., 

 in parallel arrangement, the same even low polarization and fresh glassy 

 look, are clouded in the centre by an aggregate of dots which form a 

 central area with vague boundary, but having the same polarization 

 color as the outer area. With the high power these are seen to be fluid 

 inclusions with moving bubble, little flakes of colorless mica or kaolin, and 

 black opascite masses. 



We now come to the clastic feldspars, which are generally larger than 

 those just described. Figures 1 and 2 represent typical cases. 



In Figure 1 the enlargement is fifty diameters. The feldspar polar- 

 izes in one low color and has a homogeneous extinction. One cleavage 

 is well developed in the slide parallel to the short edge ; the other, indis- 

 tinctly parallel to the right hand edge. From the obtuse angle made 

 by the two cleavages, it is evident that the section is oblique to the zone 

 of either cleavage. The outer shape of the grain, as well as that of the 

 inner cloudy portion, is evidently determined by the two cleavage lines, 

 which is some evidence of clastic character when compared with the irreg- 

 ular shape of the albitic feldspars. The cloudy look of the central por- 

 tion is owing to streaks of opaque kaolinized (f) feldspar containing fluid 

 cavities, specks of black opascite, and stained by yellow limonitic pro- 

 ducts, which lie in the clear feldspar arranged parallel to the second 

 cleavage. These are evidently areas of decomposition. As seen in the 

 figure, these bands die out in the clear feldspar rim. The whole feld- 

 spar shows in polarized light indistinct multiple twinning parallel to the 

 second cleavage, which runs almost to the outer boundary of the clear 

 rim. There occur also, scattered through the central core, little bril- 

 liantly polarizing flakes of muscovite, in part arranged parallel to the 

 first cleavage. These become less abundant, but of larger size, in the 

 clear rim, where they are apt to arrange themselves parallel to the outer 

 boundary ; near the boundary they become still larger, and sometimes 

 connect with the mica outside. The outside boundary of the whole feld- 



