366 ON THE APPARENT DISLOCATIONS [Ch. XV. 



pass at different angles, cause intersections ; and, therefore, 

 other classes ought to be instituted ; if, indeed, a character 

 which can only be discovered by extensive workings, and is 

 always subject to change, ought to be esteemed of any value 

 in a classification. The directions of the tin lodes are com- 

 monly within a few points of east and west, but there are 

 numerous exceptions : those of St. Just run nearly north and 

 south, as does also one lode in Polgooth mine ; and they must, 

 therefore, be considered not as tin lodes, but as belonging to the 

 class of cross courses. In Polgooth, also, occur veins of tin, 

 pointing, not east and west, but north-west and south-east, and 

 these contra lodes traverse and heave some regular east and 

 west tin lodes ; so that, according to the law of intersection, 

 contra lodes are sometimes more ancient than the first class or 

 the oldest true veins. We must, therefore, add to the pre- 

 sent class of tin lodes, contra, cross, and as many other classes 

 as there are exceptions. Besides, it may be stated, that veins 

 in some parts contain copper ore, and in others, these mi- 

 nerals are intermixed with the tin ; and since tin and copper 

 lodes have the same bearings, how is the class to be deter- 

 mined when such veins do not interfere with those of an un- 

 mixed character? 



In this manner, each of the classes might be considered in 

 review, and without bringing forward other facts than those 

 already on record, might be proved to be objectionable : thus, it 

 might be stated, that the more recent are only separated from 

 the oldest copper lodes, because cross courses are sometimes 

 intersected by copper veins; if this additional class had not 

 been instituted, the fifth and seventh classes would have been 

 united ; indeed, the last of these is not distinguished by the 

 miner from cross courses ; and these combined classes might 

 also have comprised the eighth or slides, since they are only 

 mineral veins which commonly run parallel with the metal- 

 liferous. 



The only generalisations that can be made concerning the 

 veins of Cornwall, in the present state of knowledge, are 



