Mac Culloch on Pitchstone. 51 



obsidian, with which it possesses, in fact, no affinity or transi- 

 tion, by its inferior hardness. For a fuller definition I may 

 refer to the various systems of mineralogy which are in the 

 hands of every one. 



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 conchoidal 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 gra- 

 nular. 



/. With a mixed fracture, the large conchoidal presenting a 

 minute additionally conchoidal surface. 



g. The conchoidal fracture covered with minute scales, so as 

 to give, on a superficial view, a porphyritic aspect. 



B. Concretionary. 



a. Flat, lamellar ; the lamellae thick or thin ; it even be- 

 comes schistose or papery, or fine scaly. 



b. Curved lamellar. 



c. Prismatic ; the prisms simple or jointed ; with plain or 

 with curved surfaces. 



d. Columnar; similarly, either simple or jointed: the con- 

 cretion is also sometimes partly columnar, and partly prismatic ; 

 or has plane and curved sides. 



e. Spheroidal ; large. This is generally combined with the 

 columnar. The small spheroidal concretionary, is arranged 

 with the pearl-stones. 



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