180 PROCEEDINGS OF THE ACADEMY OF [1893. 



one has enough light. The section as drawn shows how intimately the 

 quartz and feldspar are mixed. The two species are so commingled 

 as to indicate that they must have crystallized simultaneously, the 

 greater hardness seeming to be due to a somewhat greater proportion 

 of quartz. 



Explanation of Plates I and II. 



Figure 1. Gabbro Phonolite, Kadnor. Magnified 100 diameters 

 shows, (1) Sanidine, (2) Plagioclastic Feldspar, (3) Diallage, (4) 

 Magnetite. 



Figure 2. Gabbro Phonolite, 10 miles east of Quakertown. 

 X 100 ; (1) Diallage, (2) Plagioclastic Feldspar, (3) Sanidine, (4) 

 Amphibole, (5) Magnetite. 



Figure 3. Gabbro Phonolite, north of Quakertown, X 15; (1) 

 Diallage, (2) Plagioclastic Feldspar, (3) Magnetite, (4) Amphibole, 

 (5) Sanidine. 



Figure 4. Granulite, Pigeon Cove, Mass. Xl5; (1) Orthoclas- 

 tic Feldspar, the dark portion quartz, (3) Magnetite. 



