76 Thirty- fir st Report on the State Museum, 



themselves as richly colored bands, and are therefore more readily detected 

 from the phlogopyte itself, which only polarizes in various brownish-yellowish 

 shades. 



The form of these crystals is usually a parallelogram of which one pair of 

 parallel sides has a long extension, whilst the other pair, crossing the first at an 

 angle of about 60 degrees, is short (fig. 2). Sometimes, as it is represented in 

 fig. 3, another pair of parallel lines occurs forming a hexagon. Fig. 4 presents 

 a form in which the lines cross each other at 90 degrees. There are still other 

 combinations occurring as given in figs. 5 and 6. It will be noticed in nearly 

 all the preparations that the prisms are gradually altering in breadth, sometimes 

 tapering to the thinnest line, which afterwards slowly assumes again its pris- 

 matic form (fig. 7.) 



By means of the micropolariscope, it will be perceived that nearly all of those 

 long crystals are not single, but are in twin position. The parallelograms 

 present a series of colored lines and bands, arranged parallel to the long sides 

 of the prismatic figures. The bands are in certain relations to each other. One 

 system will polarize most brilliantly, whilst the other presents scarcely any 

 color.- 



In the Canadian mica of South Burgess, of which Zirkel has given a 

 description in his previously mentioned work, the prismatic crystals are more 

 frequent, but much smaller. Zirkel does not mention the occurrence of twins 

 in those crystals. He pronounces them to be monaxial mica, lying with their 

 bases in that of phlogopyte. 



It seems to the writer more likely that these crystals are mica sections, 

 through their lateral sides, crossing the base of phlogopyte at an angle of 90 

 degrees. In large phlogopyte specimens, sometimes even to the naked eye, 

 plates of mica are visible, which lie with their base in the lateral faces of phlo- 

 gopyte. 



In regard to the position of the above-mentioned, long band-shaped crystals, it 

 will be observed that they follow a law peculiar to themselves, and of which 

 figure 1 is a graphical representation. The crystals are placed towards each 

 other parallel to the diagonals (ad) (be) (of) or (a 1 a') (U e') (e' /'). 



Figure 8 presents two 1 crystals crossing each other at 60 degrees, and figure 

 9, two crystals crossing at BO degrees. Both prisms appear dark in a certain 

 position of the analyser towards the polariser, whilst the part where they cross 

 each other is luminous, which indicates that the crystals lie in various mica 

 planes. 



In figure 10 are shown two prisms at 90 degrees to each other having 

 complimentary colors. After rotating the polariser for 90 degrees, the colors 

 will be reversed. 



Figure 11 represents three prisms crossing at 60 degrees, which answers to the 

 diagonals (ad) (be) (of) or (a 1 d') {V e>) {e'.f). 



In figures 12 and 13 three prisms form a rectangular triangle, the ratio of the 

 perpendicular sides being, in fig. 13, 1:1 or fig. 12, 1:2, as can be easily deduced 

 from figure 1. 



The second group of enclosures, in phlogopyte from Orange county, are a 

 number of black, round or needle-shaped bodies (figure 14;, which, even with 

 a magnifying power of 670 diameters, appears as a fine dust. They occur in 

 zones with a dark nucleus in the center, which is a greater accumulation point 

 of these microliter. This name was proposed by Bosenbusch for such minute 

 bodies as are difficult to discriminate. 



The microlites appear also in straight lines and curves. Sometimes they occur 

 even in the center of the long baud-shaped crystals, but generally they pene- 

 trate the phlogopyte basis. The writer is convinced that the first cause of the 



