3O THE CHICAGO ACADEMY OF SCIENCES. 



crystallized chert. Within this rim silica in solution passed 

 by osmosis or through crevices, and formed a purer layer. 

 Finally in the remaining- cavities the pure silica was slowly 

 built up in well defined crystals the form of the mineral being 

 thus dependent both upon the purity of the mother solution 

 and upon the rapidity of deposition. When deposition was 

 slow and a change in direction of current brought new mate- 

 rial into the liquor, bands were formed, and agates resulted. 



Quartz exhibits no cleavage, has a conchoidal fracture, a 

 hardness of 7, a specific gravity of 2.5 to 2.8, and occurs in 

 nearly all colors. Its lustre is greasy or glassy to dull. When 

 pure it is transparent. When impure, opaque. Before the blow- 

 pipe it is infusible, and it is insoluble except in hydrofluoric 

 acid or caustic alkali. 



Tschermak classifies hornstone with phanero-crystalline 

 quartz on the ground of insolubility in caustic alkali. Seven 

 varieties of quartz fragments placed in a solution of sodium 

 hydrate and allowed to stand for two months gave the follow- 

 ing results: 



For rose quartz, chalcedonic quartz, chalcedony, and pure 

 chert from the lake shore, there was no appreciable loss in 

 weight, whereas for flint from England there was 0.2% 

 loss; for an impure chert from the lake shore 4% loss, and 

 and for opaline chalcedony 97% loss. Plence it would seem 

 advisable to retain Dana's classification, placing chert and 

 hornstone with the cryptocrystalline variety. 



Thin sections exhibit conchoidal fracture, apatite and uifld 

 enclosures, positive refraction, righthanded or lefthanded rota- 

 tion of the plane of polarization, and brilliant interference tints. 



While the sand upon the shore consists chiefly of quartz, 

 the following analyses show that it contains many other sub- 

 stances as well. Results of five analyses showed 16% of ma- 

 terial soluble in hydrochloric acid (such as calcite, iron oxides, 

 etc.), 0.4% soluble in sulphuric acid, and 1.35% soluble in nit- 

 ric acid. There was thus left 82% of insoluble material- 

 chiefly quartz. 



Cuprite. Cu 2 O. Regular. 



The only form of the copper oxide observed in this region 

 occurs on those specimens of the native copper which have 

 been described as having been found in the drift. No crystals 

 have come to my notice. The common properties of cuprite 



