GEOLOGICAL SOCIETY OF PENNSYLVANIA. 



371 



by metalliferous and other veins, in nearly the same man- 

 ner as the granite and clay slate in which they occur: 

 this, however, only proves their priority to those veins. 



The third order comprises all that are generally ac- 

 knowledged as true veins, especially all the lodes. These 

 may be divided into several classes, the periods of whose 

 formation appear to be diiferent. 



Before distinguishing these classes, it would be well 

 to define the terms which are generally applied by the 

 miners to the different kinds of lodes, as follows: 



By a lode, is understood a metalliferous vein. 



By cast and west lodes, metalliferous veins, whose di- 

 rection is not more than 30° from those points. 



By contra lodes, metalliferous veins, whose direction 

 is from 30 to 60° from east and west. 



By cross cou?^ses, veins whose direction is not more 

 than 30° from north and south. 



By flukan veins, veins of whitish or greenish clay, ge- 

 nerally argillaceous. 



By cross flukans, veins of this clay, having the same 

 direction as the cross courses. 



By slides, veins of slimy clay, greatly inclined, having 

 generally an east and west, and rarely a north and south 

 direction. 



Among the veins of Cornwall, where most data have 

 perhaps been collected on the present subject, and rela- 

 tive to which the facts and conclusion about to be sub- 

 mitted are principally derived ; the first class of these 

 veins, in point of age, consist probably of the oldest tin 

 lodes. Tin lodes are considered to be of two classes, be- 

 cause several instances have occurred in which, at the 

 meeting of two tin lodes, one of them is traversed and 

 heaved by the other. It may be stated, in general, that 

 the tin lodes, which underlie northwards, are traversed 

 by those which underlie towards the south. It is con- 



