SILICA. 



2G3 



Fig. 145. 



Fig. HO. 



Fig. 147 



Fig. 148. 



Figs. 130, 131, 132, 133, 1.36, 141, 142, 144, 147, 148; together with Figs. 149, 150, 1.51, 

 152, 153, 154, 155, 156, 157, 158, 1.59, 160*, and also tlie twins 140 and 161, from Mid- 

 dleville. 



Fig. 150. Fig. 151. 



Fig. 1 19. 



Fig. 153. 



Fis!. 154. 



Fig. 155. 



Fig. 15C, 



* Figures 157, 158, 159 and ICO, arc introduced on tiie aulliorily of Dr. Horton. 



