66 Mb HOPKINS, ON RESEARCHES IN PHYSICAL GEOLOGY. 



has been already shewn (Art. 17), that if a fissure in its progressive 

 formation meet with any line of less resistance, it will under certain 

 conditions be propagated along it for a certain distance, and then 

 resume its original direction. If AB (Fig. 3, p. 61) be a line of less re- 

 sistance, EC'Cn would represent a horizontal section of the fissure 

 formed in the manner just supposed, and thus presenting the apparent 

 displacement C'C". 



It must be remarked, however, that an apparent displacement due 

 to this cause must necessarily be such as represented in the figure just 

 referred to, viz. on the side of the obtuse angle EC'C", or D'C'C. 

 and not on that of the acute angle ec'c", or dc'c (Fig. 4, p. 61): 

 and we may also observe, that neither this cause, nor that pointed out 

 in the previous article, appear sufficient to account for the fact, whicli 

 has been frequently recognized, of two or more adjoining veins being 

 apparently displaced, or heaved, to the same extent and in the same direc- 

 tion by the same cross course. We see no reason why the apparent displace- 

 ments of two such veins should be related in either of these particulars, 

 when produced by the cause indicated in Art. 68 ; and if produced by that 

 mentioned in the preceding paragraph, though the apparent displace- 

 ments would necessarily be in the same direction, there seems to be 

 no reason why they should be of the same extent. When the heaves, 

 therefore, of adjoining veins appear to be related to each other both in 

 extent and direction, the above two causes do not appear to offer an 

 adequate explanation of the phenomena. 



70. It was a notion first propagated, I believe, by Werner, 

 and subsequently adopted by many other geologists and miners, that 

 when two veins meet each other, of which one is heaved, and the 

 other unbroken, the formation of the latter must necessarily have 

 been posterior to that of the former. The theory of elevatioYi, how- 

 ever, which we have been discussing, will not authorize this conclu- 

 sion. If we assume the modes of producing apparent displacements 

 considered in Arts. 68 and Q% it is evident that we must adopt a rule 

 exactly the reverse of the one just stated ; and if we suppose the displace- 

 ments to be real, it is manifest from what has been advanced in this and 



