ON THE VOLCANIC THENOMENA OF VESUVIUS. 291 



Las been a marked rise in temperatare of this neiglibourliood since these 

 cunicnli were made, as I maintain that if we, in a half hour exerting 

 ourselves but slightly, were so indisposed (in ray own case I may say 

 gravely), it would have been perfectly impossible for workmen to 

 cut out the compact tufa at the end of a narrow cuniculus just large 

 enough to allow a medium-sized man to walk upright, and to transport 

 the materials for 50m. along this hot passage, and then for another 100m. 

 along a cooler one. 73° C. was the temperature we experienced, but no 

 doubt it had been lowered by the ciiculation set up in the other branches 

 from the new railway tunnel, and the mephitic atmosphere must also have 

 been improved. There remains, therefore, but one explanation, and that 

 is that here the temperature has inci'eased during the last two thousand 

 years. I do not, however, suppose that the ground was cool, as we have 

 historic evidence that the so-called Baths of Nero, and all the district, was 

 renowned in Roman times for its thermo-mineral waters ; and the inclined 

 passages seem to indicate that they were used for bringing the water up, 

 as they are nearly all in relation with the i-uins of thermae I only main- 

 tain that the temperature has augmented considerably, and seems to 

 indicate the localization of future eruptive action to this locality. The 

 long horizontal passages I take to have been made to collect the vapours 

 for the sudatoi'ii, and the connection I have really seen to exist in one 

 place. If I am wrong in my conjecture as of general application, I am 

 open to correction by competent arch^ologists. 



The material of the whole of this first of the tunnels at Baja is com- 

 posed of a somewhat friable porous tuff, in some parts yellow, and in 

 others light green. Towards the western end the tuff is more stratified, 

 and less altered, being composed of bands of white pumice imbedded in a 

 buff-coloured dust. All the large masses of pnmice in the three varieties 

 of tuff are much altered on their surface into a white powdery substance, 

 probably kaolin. 



The second tunnel from Baja to Fusaro was made through very much 

 cooler ground, consisting of a rather loose tuff of pozzolana with masses 

 of large pumice. In this one a number of cunicnli were also cut through, 

 and two of the inclined ones I was able to examine. The first, on the left, 

 communicated with a Roman bath-room, a short distance in from the 

 Baja entrance, and on the right descended to some hot water with a tem- 

 perature of 57° C. Another one, some considerable distance further 

 along on the same side, descended to hot water of 67°. The stones at the 

 bottom of the little pond of water I noticed to be of an intense black 

 colour, and on removing these they were seen to be covered by a wet 

 sooty deposit of from 0'5m. to Im. in thickness, and smeared over at 

 spots with gelatinous silica, so as to have the appearance of wet stringy 

 mucus. Although the simile is not elegant, the appearance was such 

 that I thought, on withdrawing the first example, that some workman 

 had spat upon the stone. A qualitative analysis proves this black 

 deposit to be a hydratedox^'de of manganese; it must have been deposited 

 from a water very rich in some salt of that base. 



During last autumn dredging operations were carried on just W. of 



the wooden pier at Pozzuoli, belonging to Messrs. Armstrong's works ; 



they bi'ought to the surface upwards of forty beautifully carved capitals 



and pedestals of small columns from a point which, by tradition, was the 



ituation of the Temple of the Nymphs. 



tj 2 



