PITCHSTONE. 533 



darker hues, and the olive greens in particular, 

 are predominant. 



The ordinary transitions of pitehstone are into 

 basalt, chalcedony, and chert, as already noticed. 

 One of the varieties of chalcedonic chert thus 

 found in Arrari is of a very singular character ; 

 presenting* a spheroidal concretionary structure, 

 with an internal radiating or concentric disposi- 

 tion in the spherules, and weathering to a botry- 

 oidal surface. 



SYNOPSIS OF PITCHSTONE. 



FIRST DIVISION. 



Simple. 



A. ''Amorphous, massive. 



a. With a simple conchoidal fracture. 



b. With a flat conchoidal fracture. 



c. With a splintery couchoidal fracture. 



d. With a splintery granular fracture, and 



of various aspects, according to the 

 size of the parts, 



e. With a mixed fracture, the conchoidal 



being also granular. 



