294 EEPORT — 1889. 



one locality. Besides, the fineness of the tuff increases as we recede in 

 all directions towards the periphery of the deposit. 



My experience is that the presence of limestone fragments is limited 

 to the close jjroximity of steep slopes of that rock, and that as we increase 

 the distance from the evident source, their quantity diminishes. In 

 the same manner I found (though with some uncertainty) that the 

 amount of metamorphism was in direct proportion to the development of 

 the tuff, simply because there was more of the fluoriferous reagent to act 

 upon the calcic carbonate. 



As a further confirmation of the relative age of this grey tuff, I met 

 with a striking piece of evidence at the village of Pastena near S. Agata 

 di Sorrento ; here the tuff has been worked to a depth of three or four 

 meters, but I could not see its base. It forms fairly regular columns, 

 and is overlain by recent alluvial deposits with Vesuvian pumice. In 

 one or two places between these two deposits small pockets or depressions 

 nve filled by a breccia almost identical in components with that of Monte 

 Santo, Pianura, and Soccavo. The fragments of vitreous trachytic 

 scoria attain the size of a fist, but the more compact trachytes, solfatarised 

 tuffs and leucite lavas (rare) exceed the size of two walnuts. Some 

 of the scoria is strikingly similar to the wood-like masses above the 

 breccia at Soccavo. The breccia has all the appearances of having been 

 rearranged by water, and therefore, probably, is the equivalent of the 

 many-rock breccia, the Grifeo lapillo beds and its associated pumice and 

 ash deposits. The only difference that I could find was a somewhat 

 greater abundance of leucitic rocks. 



The other excavations in the vicinity of Naples have brought little to 

 light ; but the numerous trenches that are already commenced for the 

 new sewerage system will undoubtedly afford a large amount of new and 

 valuable evidence. In fact, the next year must be looked upon as the 

 most important up to the present, and for many years to come, as being 

 the one in which the most valuable geological facts will come to hand. 

 Those new data will, no doubt, to a great extent, settle the more impor- 

 tant questions beai'ing on the geology of this region, and some of volcano- 

 logy in general. 



Liberated as I am from the monotonous work of the mapping of 

 Vesuvius and Monte Somma, I propose to devote myself to the study of 

 these sections, and the results they afford ; and, should circumstances be 

 favourable, also to the investigation of some of the physics of fluid lava. 

 I have a large amount of material on hand, but await publishing this 

 until further excavation confirm or modify the conclusions drawn there- 

 from. Many of these important discoveries will be open to the party of 

 English and foreign geologists, who will visit this district immediately 

 subsequent to the present meeting. This excursion, the first of its kind, 

 has been organised at my instigation by that active body, the Geologists' 

 Association, in conjunction with the Geological Societies of London and 

 Italy, and under the hospitable patronage of the Italian Government, and 

 esjDecially the Minister of Public Instruction, Signer Boselli. 



