BOOK V. 



103 



divide it obliquely ; howcviT, my discourse is now concerned mainly with 

 vena pro/ioulu, but most of all with the metallic material which it contains. 



Three vertical shafts, of which the first, A, does not reach the tunnel ; the 



SECOND, B, reaches THE TUNNEL ; TO THE THIRD, C, THE TUNNEL HAS NOT YET BEEN 



DRIVEN. D — Tunnel. 



