OK COAL. 



fkct which might be stated as inconsistent with 

 the idea of these veins having been formed with- 

 out previously existing rents, if we did not know 

 that similar shifts occur in cotemporaneous groups 

 of crvstals. 



9. Some cotemporaneous veins are crossed in 

 part of their course by a portion of the stratified 

 matter in which they are contained : thus, veins 

 of granite or gneiss are crossed by portions or thin 

 beds of the gneiss. This fact is illustrative of 

 the formation of veins without previously exist- 

 ing rents. Similar appearances occur in crystals, 

 as in those of schorl and tremolite. The metal- 

 liferous veins in the Derbyshire limestone, which 

 are frequently interrupted by beds of trap, ariS 

 probably appearances of the same kind. 



in. Oil Coal 



The generally received opinion in regard to' the 

 formation of this substance, is, that it is vegetable 

 matter more or less changed by natural processes 

 but little known to us. But the occurrence of 

 coal in primitive country, where no organic re- 

 mains have hitherto been discovered, and the par- 

 ticular geognostic relations of this mineral, incline 

 me to believe, that glance -coal, and also black-coal, 

 are original chemical deposites, as little connected 

 with vegetable remains as the shells. Sec. in lime- 

 stone, are with the limestone in which they are 



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