on " Researches on Phi/sical Geology.'" 369 



fact, established by his own observation, the general coinci- 

 dence of their directions; and this general coincidence, which 

 seems equally to have struck Dr. Boase and myself, is pro- 

 bably all that the theory of the formation of veins in joints 

 would require. If we could descend into any master joint, 

 and follow its course, we should no doubt find it frequently 

 intersected by other joints, some of them belonging to other 

 cross-systems, and others more partial and irregular. The 

 continuity, however, of a cross-joint through the matter of the 

 vein itself I should think a rare occurrence in our limestone 

 districts, and I confess that I should be much surprised to 

 find such to be anything like a general rule in the Cornish 

 lodes. That such cases might occui", and not very unfre- 

 quently, appears very possible, because it is probable, I think, 

 that the process of the formation of joints was one of loner 

 duration, and might be continued after die segregation of 

 many of the Cornish lodes into the earlier joints; and more 

 particularly, perhaps, might this be expected in those cases 

 in which the causes producing joints have acted with the 

 greatest intensity, which appears to have been in the older 

 rocks. It must be understood too that I here speak of the 

 absolute continuity of a particular ^ozW, not of the general 

 directions of cleavage of the mass. It would appear bv no 

 means improbable that the matter deposited in an open fissure 

 should become subject to the same kind of action which mioht 

 have previously produced a laminated structure in the sur- 

 rounding mass. This presents, I conceive, no difficulty, be- 

 cause it does not necessarily lead to the inference that this la- 

 minated structure in the vein must have been superinduced 

 contemporaneously with that in the containing mass, an in- 

 ference which might be drawn from the continuity of distinct 

 joints through the lode itself 



With respect to what Dr. Boase appears to consider a re- 

 ductio ad absurdum, it is manifestly unnecessary to say any- 

 thing in direct reply, except what I have before stated, that it 

 is totally inadmissible to assume the earth's crust to have 

 become jointed before the action of the dislocating force 

 upon it. 



In what I have now advanced respecting these theories of 

 the formation of veins, and of their relative claims to our ac- 

 ceptance, I would beg to be understood as speaking with re- 

 ference to existing evidence. With respect to the limestone 

 districts I can feel little doubt of the result of moie extended 

 investigation. How far the two methods of formation will be 

 found ultimately satisfactory as applied to the whole of the 

 Cornish veins, I pretend not to say with equal certainty. It 



Third Series. Vol.9. No. 5o. Nov. 1836. 2 X 



