OP ARTS AND SCIENCES. 41 



The Damourite and Sterliugite are types of a very large class of 

 hydrous micas, which in many places are widely distributed through the 

 granitic rocks. This class of minerals has been especially investigated 

 by Professor Haughton, of Dublin, whose papers may be found in Phil. 

 Mag., IV. ix. 272, and Q. J. G. Soc, xviii. 414, also xx. 280. We cite 

 here a few of his analyses, selected from those given by Professor 

 Daua,— pages 310 and 311, of the fifth edition of his "System of 

 Mmeralogy," — in further illustration of the subject we are discussing : 



Dublin Co. — Haughton. Optical Angle, 53°. 



Si Al Fe Mg Ca Na E H 



43.47 31.42 4.79 1.13 1.38 1.44 10.71 5.43 = 99.77 

 23.18 14.64 1.44 0.45 0.39 0.37 1.82 4.83 



23.18 1G.09 3.03 4.83 



' , ' 



23.18 16.09 7.86 



3. 2. 1. 



Mt. Leinster. ^- Haughton. ' Optical Angle, 72°. 



Si Al Fe Mg E H 



44.64 30.18 6.35 0.72 12.40 5.32 = 99.61 



23.81 14.07 1.90 0.29 2.11 4.73 



23.81 15.97 2.4 4.73 



23.81 15.97 7.13 



3. 2. 1. 



Glendalough. — Haughton. Optical Angle, 70°. 



Si Al Fe Mg Ca Na EH 

 44.71 31.13 4.69 0.90 1.09 1.27 9.91 6.22 = 99.92 

 23.84 14.51 1.41 0.36 0.31 0.33 1.68 5.53 



23.84 15.91 2.68 5.53 



23.84 15.91 • 8.21 



3. 2. 1. 



In these micas again, if we regard the water as basic, we obtain a 

 nearly constant ratio, but differing from that of Damourite in the 

 relation of the two basic radicals. The general symbol of the last 

 would be : — 



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