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MB. Or. W. TYRRELL ON THE 



[vol. lxxii, 



descriptions (see Tables I, III, and V). Eef erring to these it 

 may be seen that lime-soda felspar attains its maximum develop- 

 ment, 34*5 per cent., in the teschenites. It dwindles steadily 

 through the theralites, lugarites, and picrites, and is absent from 



the peridotite. Orthoclase occurs most abundantly in the tesch- 

 enites, but is present in small amount (although unrecorded) in all 

 the other rocks, save picrite and peridotite. It is a mineral hard 

 to detect and measure when associated with abundant lime-soda 

 felspar, but its presence is demonstrated by the potash of the 

 chemical analyses. Analcite is the characteristic mineral of the 



