ORIGIN AND DEVELOPMENT OF ORE DEPOSITS. 143 



Henry Delabeche in his "Report," already quoted, illustrates 

 by diagrams how a lode may be apparently although not really 

 heaved by an elvan course. Many such cases are known in the 

 West of England, and it may be worth while to reproduce his 

 figure and remarks thereon. "Let«. b. fig. 13, Plate X, represent 

 an elvan, and d. e. a lode formed subsequently to it. Without due 

 care and examination it might be assumed that the elvan a. b. was 

 introduced into a fissure formed after the lode d. e., heaving it at 



c In the same way a lode may be apparently heaved 



while passing from slate into granite, arising from the fact that 

 the plane of junction is more easily divided for a short distence 

 than the direct line of fracture followed."* Such apparent heaves 

 very rarely occur in cases of intersection where the intersecting 

 veins form large angles with each other, or where they have 

 very different or opposite angles of underlie. Moreover in most 

 cases of true heave, indications of what we have termed "drag" 

 occur, which are wanting in the cases we now refer to, so that if 

 a little care be taken there is not much likelihood of such 

 apparent heaves being mistaken for true heaves when the actual 

 intersection is visible. 



As already mentioned, such complex fissures are most likely 

 to be formed when the angles included by the intersections of 

 the veins are small, as in the case just mentioned, but some at 

 least are known where the intersecting veins form angles near 

 to 90°. In such cases however, the heaves are rarely large. 

 One such appears to have been worked on at South Spearn Mine, 

 in the parish of St. Just. Here the Noon Reeth Guide seems 

 to be carried by the Lane lode, but really passes alongside of it 

 for a distance of 50 fathoms. f In all such cases as those given 

 above, the apparently heaved lode seems to be actually the 

 older, and to have been really heaved as regards the original 

 fissuring, whether its mineral filling traverses the heaving lode 

 or not, but the traversing deposit is undoubtedly the newer. 



*Delabeche Report on Cornwall, Devon, &c, p. 299. 



fWith reference to this, Mr. Henwood remarks that "the lode contained 

 neither tin nor copper while running in the direction of the guide. This of itself 

 seems to shew that the 50 fathoms in question were really part of the complex 

 fissure of the guide. It is not improbable that the corresponding portion of the 

 lode is still standing unworked at some small distance to the northward. 



