536 PITCHSTONE. 



g. Porphyritic : but the grains, which are 

 chiefly of quartz and chert, are fur- 

 ther condensed in lamellae which 

 alternate with a slightly porphyritic 

 pitchstone. 



THIRD DIVISION. 



Concretionary spheroidal : Pearlstone. 



A. Consisting of simple pitchstone; the grains 

 irregular, and compressing each other in the manner of 

 coccolite. 



B. Some, or all of the grains, containing a central 

 substance of another kind : pearlstone porphyry. 



a. With grains of felspar, or of felspar and 



enamel, or of enamel only. 



b. With quartz, or quartz and chert. 



c. With quartz and felspar both. 



d. With a central atom of clay. 



THIRD DIVISION. 



Amygdaloidal : containing- imbedded nodules 

 of another mineral. 



A. Pitchstone containing imbedded zeolites. 



As yet this variety has occurred only in Baffin's 

 Bay. 



The colours of pitchstone are various. They 

 are, principally, dull white, pale ochre, pink, pale 

 green, greenish grey, ochre yellow, ochre ped, 



