202 RECORDS. 



The exogenic or clastic rocks were divided into autoclastic, 

 hydroclastic, pyroclastic, bioclastic and anemoclastic. 



A further subdivision according to texture was, into ruda- 

 ceous or conglomeratic, arenaceous or sandy, and lutaceous or 

 mud rock. 



The next division was according to composition, into two 

 main groups — silicious and calcareous ; and finally into un- 

 consolidated and consolidated and metamorphic rock. 



In the discussion of the paper Professor Stevenson spoke of 

 the value of such a classification through its giving teachers 

 ideas for presentation to their classes regarding the interrela- 

 tions of rock. Professor Kemp spoke of the system being 

 well adapted to geologic study on account of its giving the 

 surroundings in which any specified rock has developed, 

 although it is not practicable to assign a place to every small 

 rock group which is really of mineralogical rather than of 

 geological value. 



Mr. Levison said : Fluorescence or the property of increas- 

 ing the wave-length of certain luminous rays enhances the 

 beauty of a few colored gems under conditions which lessen the 

 effectiveness of others that do not possess this property. Gar- 

 net, for instance, which is non-fluorescent, loses its rich crimson 

 color and becomes dull gray in pure blue light. On the con- 

 trary, most kinds of ruby and ruby spinel, and pink topaz 

 respond to light-rays above the red on account of their fluores- 

 cence, and in blue-violet light still display their characteristic 

 tints. The red color of the ruby is somewhat developed by the 

 light of the air-gap spark and an uncovered Crookes tube. It 

 is intensely excited by the cathode rays. Willemite displays a 

 beautiful greenish-yellow color not only in ordinary light rich 

 in the yellow-green rays but also in light consisting chiefly or 

 wholly of the more refrangible colors in which its characteristic 

 color would be effaced but for the possession of fluorescence in 

 high degree. This mineral is excited furthermore by some of 

 the ultra-violet rays and by the Roentgen and Becquerel rays. 



Other materials which owe desirable tints to fluorescence are 

 pearl, opal, hyalite, chalcedony and kunzite (the new Ulac spo- 



