SILICA. 
263 
Figs. 130, 131, 132, 133, 136, 141, 142, 144, 147, 148; togetherwith Figs. 149, 150, 151, 
152, 153, 154, 155, 156, 157, 158, 159, 160*, and also the twins 140 and 161, from Mid- 
dleville. 
Fig. 150. Fig. 151. 
* Figures 157, 158, 159 and 160, are introduced on the authority of Dr. Horton. 
