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I. Andalusite-bearing mica-slate ; 100 ft. from junction. 



II. Schist ; 50 ft. from junction. 



III. Schist; 15 ft. from junction. 



IV. Tourmaline-hornfels ; 1 foot from junction. 

 V. Tourmaline-veinstone. 



VI. Albany granite. 



These analyses show that silica, boracic acid, fluorine, and probably 

 also soda, have been added to the schist. 



MlNEKALS OF THE CONTACT-ROCKS. 



Andalusite. When this mineral occurs in more or less definite 

 crystals it possesses a columnar habit. The crystals are elongated in 

 the direction of the vertical axis. The crystals are, as a rule, bounded 

 by the forms (110) and (001). The prismatic angle is 90 50', so 

 that cross sections are very nearly rectangular. The a axis of 

 elasticity is coincident with the length of the crystal and is also 

 the acute bisectrix, so that the double refraction is negative. Longi- 

 tudinal sections are lath-shaped and give straight extinction as the 

 mineral is orthorhombic. Cross sections extinguish when the short 

 axes of the nicols bisect the angles formed by the faces of the 

 prism. The most perfect cleavages are parallel to the prismatic faces. 

 These are sometimes recognizable in thin sections, sometimes not. An 

 interesting feature of andalusite is its pleochroism. This is very often 

 unrecognizable in thin section, and when it is recognizable it is 

 generally distributed throughout the mineral in an irregular manner; 

 certain portions showing the phenomena much more decidedly than 

 others. In pleochroic crystals the phenomena are seen best in the 

 longitudinal sections. Rays vibrating parallel to the a axis (vertical 

 axis) are red ; those vibrating parallel to the ft and 7 axes are 

 colourless or pale green. 



In transverse sections containing the ft and 7 axes no distinction 

 of colour can, as a rule, be recognized in the ordinary thin sections. 

 The refractive power of andalusite is higher than quartz ; the double 

 refractive power is about the same as quartz. In a large number of 

 contact-rocks the mineral occurs without form. It then generally 

 contains a large number of rounded grains of quartz which look 

 like holes. These rounded grains are often so numerous as to bear 

 about the same relation to the andalusite-substance as the holes do 

 to the fabric in a piece of embroidery. Refraction, double-refraction 

 and pleochroism are the only characters available for the recognition 

 of the mineral when it occurs in this condition, and the last- 

 mentioned character is often wanting. Andalusite often contains other 

 minerals besides quartz as inclusions (e.g., brown mica and magnetite), 

 and it frequently happens that the arrangement of the minerals in 

 the andalusite stands in direct relation with the arrangement of the 

 minerals in the rock-mass. Lines of magnetite grains may, for example, 

 be sometimes followed through a crystal of andalusite. As a general 

 rule however, the crystallization of the andalusite appears to have 



