THE MONTEREGIAN HILLS 259 



is distinctly the most abundant, except in the finer-grained 

 variety forming the summit of the mountain in which it is dis- 

 tinctly subordinate in amount to both pyroxene and mica. It is 

 deep brown in color and is sometimes hypidiomorphic in its 

 development, but often occurs with perfect crystalline form, 

 showing the prismatic and the orthopinacoidal faces. Its extinc- 

 tion is larger than is usual in brown hornblendes, judging from 

 the recorded instances, reaching 20°. It possesses a strong 

 pleochroism as follows : 



a = pale yellowish-brown. 

 b = deep-brown. 

 C = very deep-brown. 

 Absorption = C :^ b > a. 



It is often twinned parallel to 00 P 55 or to a steep orthodome, and 

 sometimes presents a faint zonal structure, marked by a slight 

 difference in extinction of the several zones indicating a slight 

 change in composition as growth proceeded, and occasionally a 

 greenish tint is noticeable about the margin of the individual. 

 It sometimes holds inclusions of magnetite and is often inter- 

 grown with the pyroxene. In the essexite from one place on 

 the south side of the mountain, the hornblende was found free 

 from inclusions, and practically free from the pyroxene which is 

 usually so intimately associated with it. From this locality a 

 quantity of the hornblende was obtained in a state of perfect 

 purity through repeated separations by means of Klein's solution, 

 all grains of foreign mineral still remaining being finally removed 

 by picking them out by hand with the aid of a powerful lens. 

 The pure material thus obtained was analyzed by Professor 

 Norton Evans, of the McGill University, every precaution to 

 secure accuracy being observed and especial care being taken 

 to effect a complete separation of the magnesia from the alumina 

 by the repeated precipitation of the latter. The water was esti- 

 mated by a direct determination. The results of the analysis 

 are given below, together with those of several other hornblendes 

 of similar composition which have been added for purposes of 

 comparison : 



