Mh HOPKINS, ON RESEARCHES IN PHYSICAL GEOLOGY. 79 



we^^have already described as the consequence of a general elevatory 



Since the existence of joints in rocks appears to be very general 

 It becomes a matter of interest to enquire what effect they mfy pos-' 

 sibly have had m determining the positions of the lines of disloLL 

 which we at present observe in the crust of the globe as aJreX' 

 descn ed. Our present limited knowledge of the exten't of jo nts orf 

 zontally and verticaUy, and of their relative directions, will not enable 

 us to return any direct and definite answer to this enquiry. We mav 

 however observe (and the observation is important as respects the J. 

 phcabihty of th,s theory) that in those districts where the directions 

 of faults, mmeral veins, cross courses, &c., bear those relations to a well 

 defined axis of elevation, which would exist according to these theo 

 retical views and which observation, so far as it ha^ proceeded has" 

 shewn to hold very generally, it would appear absurd to as^'n thos" 

 directions to the influence of joints, unless some cause can also be 

 assigned why the elevatory force should act in such a manner as to 



Zl :f ::r ^V^'^-' ^ ''"^*'^" "^^^""-^ ^ ~y relation o 

 that of any previously existing system of joints. As it appears ■,! 



iTelZ^t'uir ^""^'r '^"^ ^""^ ''-' '- '-^' ' thinHSiout- 

 he itation, m the cases above-mentioned, reject the hypothesis of anv 



extensive influence of a jointed structure upon the phenomena in 



question. Should a general coincidence be hereafter observed in the 



directions of jomts, and those lines of dislocation which foUow t le 



laws before mentioned, it would seem far more probable, that the 



X'lena " '"''"""^ ""' ''' ''""' ^'"^ '''' '^'''^ ^^ ^he former 



In asserting the generality of the laws above mentioned, it must 

 not be supposed that we are assuming the absence of aU exceptions 

 or that the directions of mineral veins may not, in some instances" 

 Imve been determined by causes different from those we have been' 

 considering. This. I think, has been unquestionably the case in the 

 veins or lodes of St Austle moor, in Cornwall, where we recoa-„i;,e 

 systems of lodes forming acute angles with each other, and obviously 



