PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 443 



Shale. Conglomerate. Sandrock.] 



An arsenide of silver, dark gray to massive, dull, often porous and crumbly. 

 Described by Dr. Wurtz, this mineral consists of two varieties. The two were 

 analyzed together, and while essentially an arsenide of silver, contained some 

 antimony, mercury, sulphur, cobalt, nickel, iron, zinc and water. The mineral is 

 sub-sectile, sub-malleable, and has a hardness about 2.5. N. H. w. 



No. 597. SHALE. 



Silver Islet landing. 



Ref. Annual Report, x, page 56. 



Meg. This red and buff fissile shale is conglomeratic below, and has a thickness 

 of forty feet. No section. 



Aye. Upper Cambrian. N. H. w. 



No. 597 A. CONGLOMERATE. (Cfierty.) 



From the bottom of No. 597. 

 Ref. Annual Report, x, page 56. 



Meg. The general aspect is fine-grained, both of the fragments and of the 

 matrix. Siliceous, calcareous and gray, blotched with angular chert pebbles from the 

 size of a pin-head to two inches in diameter, this rock represents apparently a non- 

 conformable passage from some part of the Keweenawan to a later formation. 



Mic. The section is very fine grained. The cement is partly of calcite, but 

 siliceous spherules which give a black cross, and rhombic sections that are probably 

 of calcite, are scattered through it. Except for these forms the section appears like 

 a fine fragmental chert. Two sections. 



Age. Upper Cambrian. N. H. w. 



No. 598. SANDROCK. 



From a stratum thirty-five feet thick, underlying No. 597. 

 Ref. Annual Report, x, page 56; Bulletin vi, pages 123, 420. 



Meg. Light-red dolomite, sandrock, mixed with red sandrock. 

 Mic. Fragmental quartz grains compose the bulk of this rock, the cement being 

 colored by iron. One section. 



Age. Upper Cambrian. N. H. w. 



No. 599. CONGLOMERATE. (Pebbly.) 



From a stratum lying below No. 598; five feet thick. 

 Ref. Annual Report, x, page 56. 



Meg. The pebbles are well rounded by beach action. Many of them are red, 

 appearing to be of taconyte. This rock resembles the Puckwunge conglomerate, and 

 perhaps holds the same chronologic place. 



Age. Potsdam(?) N. H. w. 



