568 CHERT. 



As it sometimes originates in secondary lime- 

 stones, in this latter case it might be expected, 

 like the associated siliceous schists, to contain 

 organic remains ; but these have not yet been 

 discovered in it. That fact however need excite 

 no surprise ; as, in those cases where the second- 

 ary limestones lose the stratified disposition and 

 earthy texture, so as to become massive and crys- 

 talline, these bodies invariably disappear. 



SYNOPSIS OF CHERT. 



FIRST DIVISION, 



Simple. 



A. With an earthy aspect resembling that of the 

 secondary limestones ; the fracture rough., scarcely 

 granular. 



B. With a similar dry aspect ; the fracture splin- 

 tery, passing to the next variety. 



C. With a distinctly conchoidal fracture. 



D. With a laminated structure. 



E. With an internal spheroidal structure, scarcely 

 discoverable except after weathering. 



