BY W. H. TWELVETREES AND W. F. PETTERD. 25 



we know, to this part of Tasmania. Its unexpected dis- 

 covery may be placed to the credit of the yomig and 

 expanding science of microscopical petrology.* 



* Since writing the above we have seen Prof. Rosenbusch's new work 

 on the Elements of Petrology (Elemente der Gresteinslehre. 1S98), in 

 which he groups the trachytes and quartzless porphyries (orthophyres) 

 in one family. He says. (pp. 26r)-6), " Orthophyres differ from trachytes 

 only in their greater age and consequent inferior preservation, viz., in 

 the more frequent red and brown color, diminished porosity of the 

 ground-mass, dull aspect of the felspars and extreme decomposition of 

 the colored constituents. Fresh orthophyres cannot be distinguished 

 from trachytes." Referring to the sanidine in orthophyres, he adds, 

 (p. 266) : — •• In the quartzless porphyries sanidine has mostly, though 

 by no means always, surrendered its glassy habit, and possesses the 

 habit and often the red color of orthoclase." 



