125 



undulated on a small scale, or curved oh a 

 large. 



The schistose and the fibrous structures are 

 sometimes united. 



The schistose structure exists only in strata. 

 Organic remains are often united to it ; or they 

 are imbedded in the schistose rocks. 



FIBROUS. 



This structure is not common, and occurs 

 only in argillaceous schist and in limestone. In 

 the latter case, it might perhaps rather be con- 

 sidered as the result of crystallization, and as 

 claiming a place with the varieties of texture. 



It is sometimes simply parallel ; being more 

 or less distinct and straight, or curved. 



The fibres sometimes assume a sort of rami- 

 fied appearance, 



: * 



SPHEROIDAL, 



Under thi general term, are comprised all 

 the varieties of concretionary structure, which 



are neither fibrous, prismatic, nor laminar. 



\ 



The forms of such concretions are therefore 



