BOOK V. 



103 



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

 vena profunda, 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. 



