PLATE XVII. 
Fig. a. — Broken feldspar crystal in quartz-porphyry, Specimen 177, Slide 6b. 
Old Furnace road north of the junction with the Gladhill's road. In polarized 
light, X 115. 
Fig. b. — Quartz-porphyry. Specimen 25. Slide 64. Artesian well near Clermont 
House. In polarized light, X 28. 
It is attempted in this figure to show the continuity of orientation of a quartz 
phenocryst with the micropoikilitic area surrounding it, and to show (in a very 
crude way) the patchy effect given to the groundmass hy the micropoikilitic struc- 
ture. The quartz areas are bordered hy sericite scales. 
100 
