290 KEPOET — 1889. 



otter spots occur crusts of finely crystalline gypsum. Of the two 

 branches of the long cuniculus the lower terminal one exhibits a few 

 deposits of hyalite, gypsum, and carbonates of potash. It is, however, the 

 upper branch, or really the continuation, of the main cuniculus, though 

 at a higher level, that is of the greatest interest. The whole length is 

 covered with saline crusts, ranging from 1 to 10 cm. in thickness. This 

 thickness does not repi'esent the entire thickness that has been formed, 

 for on the floor one scrunches through a considerable thickness of old 

 crusts that have become detached, and are now replaced by new ones. 

 Most of the material, so far as a few qualitative tests go, that I have had 

 time to make, shows the principal part to consist of carbonates of potash, 

 with some soda, traces of H2S04 and HCl. There are certainly two, if 

 not three varieties of difTerent hydration. The crusts are all crystalline, 

 but of a fibrous character, so that the crj'stalline form is not discernible, 

 although I do not despair of detaching a few minute but measurable 

 crystals. In some parts of the cuniculus, the walls, floor, and roof were 

 covered by a capillary deposit, the flexible filaments attaining 3 to 4 cm. 

 in length. 



This upper bran ch-cuniculus terminates by a passage descending nearly 

 at an angle of 45°, but for only 2 meters. Whether this extended fur- 

 ther, or has been blocked by a collapse of the roof, is not easy of determi- 

 nation, as the whole is very thickly covered by the saline crusts. 



The temperature in this upper cuniculus I found to register 73° C, 

 though now the ventilation must be improved by the two other branches 

 having been put in communication with the new railway tunnel. 



At the time this temperature was taken I was unwise enough to 

 attempt to photograph the interior by magnesian light, I was accom- 

 panied by one of the boys accustomed to the great heat of the railway 

 tunnel. Various attempts were made to illuminate such a long narrow 

 passage, but I regret to say unsuccessfully. Although perfectly naked, a 

 stay of over half an hour in this temperature so exhausted us that when 

 we retired to the main cuniculus, where the temperature was much 

 lower, I became almost insensible, my heart and arteries throbbed vio- 

 lently, and yet I could hardly move a limb from extreme weakness. I 

 remained in this state for some considerable time until sufficiently re- 

 covered to partly dress and get to the open air ; the effort to do which 

 brought back all the symptoms, and I only recovered after drinking 

 freely of some strong wine brought me, and taking some food. My 

 porter, habituated to these high temperatures, suffered very much, but 

 recovered quicker. The symptoms I am inclined to atti-ibute to carbonic 

 acid, as after a short time there we were much troubled by tingling 

 of the conjunctiva. The proportion could not have been great, as the 

 nasal membrane did not smart ; we felt no immediate difficulty of breath- 

 ing, and our composite candles burnt freely, although they gradually 

 melted down. I am accustomed to the sensation of entering an atmo- 

 sphere of carbonic acid, and so far as I could judge, this was the cause of 

 our indisposition. That it was not simply heat is proved by the boy 

 suffering, although accustomed to even a higher temperature for longer 

 periods. 



I have gone into these symptoms as having an important bearing on 

 the volcanological history of this spot. In the first place, the Baths of 

 Nero pi'ove to us that this point has undergone a similar oscillation of 

 level to that of the temple of Serapis or Pozzuoli ; in the next, that there 



