113 



such cases, they pass into the form of non-per- 

 sistent and extenuated strata* 



Nodules are frequently imbedded in stratified 

 rocks ; but they are also found in granite. Ser- 

 pentine presents an example of this last case. 



The size of these masses varies from a foot to 

 a mile or more. 



As yet, limestone, serpentine, and compact 

 felspar, alone, have been found in this form, which 

 must be considered rare. 



VEINS* 



Veins are distinguished by their laminar, or 

 filamentary forms, and by intersecting all the other 

 forms in which rocks are disposed. They also in- 

 tersect each other. 



The course of a vein is sometimes straight, or 

 in one plane ; at others it is curved, or even bent 

 at an angle ; but the latter occurrence is rare. 



The flexures of a vein are sometimes such as 

 to amount to undulation ; rarely to contorsi on, ex- 

 cept in the case of quartz and carbonat of lime, 

 which are scarcely to be enumerated with, pro- 

 priety among rock veins. 



