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ceous schist, and in sandstone. They are dis- 

 tinguished from the rock veins above described, 

 by their nature, by their connections, and by the 

 limited extent of their connections. 



Rock veins can often be traced to some irre- 

 gular mass. In other cases, it is impossible to 



discover these connections, from the difficult or 







incumbered nature of the surface. It is presumed 

 nevertheless, that they are in every instance thus 

 connected ; as no unquestionable example of an 

 independent and insulated rock vein has yet been 

 discovered. 



The veins which have been called contempora- 

 neous, are enumerated among the varieties of in- 

 ternal structure. 



Conglomerate veins appertain more nearly to 

 the class of mineral veins, and do not find a place 

 in this division of the subject. One or two ex- 

 ceptions, it is true, have occurred, of conglomerate 

 veins not appertaining to that class ; but they are 

 considered in another part of this arrangement. 



