PLATE VII. 



FIG. i. COMMON CRYSTALLINE QUARTZ AT LEFT; CHERT AT. RIGHT SHOWING CRINOID 



STEMS AND OTHER ORGANIC' AGENTS ACTIVE IN ITS FORMATION. 





FIG. 2. GEODE IN NIAGARA LIMESTONE AT LEFT; QUARTZ CRYSTALS AT RIGHT; UPPER 

 SPECIMEN SHOWS PRISMS CAPPED BY RHOMBOHEDRONS. 





