144 ORIGIN" AJSTD DEVELOPMENT OE ORE DEPOSITS. 



On the other hand there is no doubt that very many of the 

 smaller "apparent heaves" are nothing more than contempor- 

 aneous fractures, with a considerable shift among the various 

 fragments.* Such movements may be particularly well traced in 

 many stock-works, as for instance at Polberrow, in St. Agnes. 



It is not the object of these papers to explain all the 

 phenomena of faulting; enough has been said on this subject, if 

 it be understood that in the West of England, as in all other 

 mining localities, neaily the whole mechanical phenomena of the 

 intersections may be clearly accounted for by considering the 

 hanging- wall side to have descended, the rocks taking up more 

 room laterally so to speak, so as to close up and occupy space 

 left vacant by shrinkage and contortion. In a few instances, 

 perhaps 3 per cent of the whole, reverse action has taken place, 

 the rocks being faulted while under lateral compression so that 

 the hanging wall has ascended in relation to the foot-wall. In 

 very rare cases there are evidences of a descent of the hanging 

 wall at one end of a fissure, and an ascent at the other, due to a 

 movement of revolution in the mean plane of the fissure around 

 some intermediate point. 



Junction faults. The junction of granite and killas in the 

 West of England often affords distinct evidence of faulting, and 

 sometimes on a considerable scale. Near Ashburton, a lode is 

 marked on the geological map which coincides for a considerable 

 distance with the direction of the junction of granite and killas. 



According to Mr. Henwood, many of the lodes of the 

 Oaradon district have granite on their foot walls, and slate on 

 their hanging walls.f 



Very similar phenomena have been observed in connexion 

 with the "Great Flat Lode," which is pretty accurately 

 coincident with the line of junction of the Cam Brea granite 

 where it touches the slip of slate which lies to the southward 



*Delabeche, Report, &c, p. 297. 



f" It seems therefore that whether the lodes of this district dip N. or S., the 

 shallower parts of their upper (hanging wall) side are of slate, wbilst the immedi- 

 ately confronting portions of their lower (footwall) as well as both their sides 

 (walls) at greater depth, are of granite." Henwood, Trans. Geol. Soc. Corn., 

 vni, p. 660, 



