62 Mr HOPKINS, ON RESEARCHES IN PHYSICAL GEOLOGY. 



intersect a third, both are apparently shifted horizontally, but in opposite 

 directions, presenting the appearance represented in the preceding diagram 

 (4), (a horizontal section), where C"D and c"d' are apparently so shifted, 

 though it is manifestly impossible that they should be so heaved by 

 any horizontal displacement of the mass containing them. 



This case admits, however, of a perfectly simple explanation on the 

 hypothesis of a vertical motion, provided the two veins, which are 

 apparently shifted, hade or underlie in different directions. This will 

 be immediately seen by a reference to the diagram (2), where dec" repre- 

 sents the plane of the second vein "intersected by AB in the higher 

 portion of the mass, and c'eg in the lower. The line cc' being parallel 

 to CC, it is manifest that when C coincided with C, c' would coincide 

 with e; and consequently, after the denudation above supposed, the 

 intersections of these veins Avith the exterior surface will present the 

 ap])earance represented in (Fig. 4). 



64. The case just described is admirably calculated to afford a 

 decisive test, as to whether these phenomena have, or have not been 

 produced by vertical movements, or rather by upward movements parallel 

 to the plane of the unhrohen vein. It is manifest that the explanation 

 above given depends on the fact of the veins CD, cd, inclining in 

 opposite directions, or more correctly, upon their intersecting the 

 plane of the vein AB, in lines inclining towards each other from the 

 parallel lines CC, cc' respectively. Consequently, it may be stated in 

 general terms, that if the two shifted veins incline in the same direction, 

 the above explanation is inadmissible: but if, on the contrary, it be 

 found that these displacements in opposite directions occur only in 

 veins which hade in opposite directions, the truth of the explanation 

 can no longer admit of a reasonable doubt. 



'&"- 



65. Other cases also of the apparent displacement of a single vein, 

 may afford most valuable evidence respecting the fact of the kind of 

 elevation of which we have spoken. It is manifest, that whatever the 

 case of displacement may be, the horizontal extent of it must depend 

 on the following quantities : the inclinations of the planes of the broken 

 and unbroken veins to the horizon (the complement of the angles wliich 



