ON THE VOLCANIC PHENOMENA OF VESUVIUS. 



289 



been encountered crossinj^ the tunnel at various angles and at different 

 levels. Many of thepc are inclined passages, just large enough for a man 

 to descend, quite similar, in fact, to those at the Batbs of Nero. Where 

 these passages reach the drainage level, they are filled by hot mineral 

 water. The tunnelling continues on for some distance beneath the water, 

 so that it is impossible to know how the original excavation terminates. 

 The present state shows that we have confirmatory evidence of subsi- 

 dence since Roman times. Others have a horizontal course and extend into 

 the hills, for in some cases over 100 meters. One of these was in sufficient 

 repair for careful observation. It enters the mountain near the road to 



Fig. 5. — Diagram of the Summit of the Great Yesuvian Cone, August 2G, 1889. 



N 



Lettering as in former Figures. 



Baja, and close to the first pozzolana quarries, after passing the Baths 

 of Nero, and follows a perfectly straight course, till it reaches jast above 

 the top of the railway tunnel. About 50m. before its termination it 

 divides into three, one of which descends and terminates in a very hot 

 water, just beneath the railway tunnel. The other two branches run one 

 above the other, the lower of which, after a short distance, turns suddenly 

 to the right or E., and descends almost perpendicularly to join another 

 cuniculus, which, running backwards towards the road, soon divides into 

 two, but is choked by the falling in of the roof. This last presents thick 

 incrustations on its walls, and on a rubble- wall support, put in at one 

 place, at a later date, thick deposits of hyaline silica, which in some cases 

 is crystalline, presenting apparently very minute crystals of quartz ; at 

 1889. o 



