304 PROF. G. DE LORENZO OX THE HISTORY OF [Aug. 1 904, 



fairly-numerous fragments of other tufaceous rocks and lavas, with 

 a few infrequent fragments of felspar and pyroxene-crystals. 

 Among the rock -fragments, the most prevalent is a greenish tuff, 

 very similar to the Epomeo tuff, which has also been met with, in 

 place, below the yellow tuff in the artesian well of the Royal 

 Garden. Trachytic black scoria?, too, are scattered abundantly 

 through the yellow tuff, diminishing in size as the distance of the 

 exposure from the vents whence they were erupted increases, and 

 being therefore smallest at the outermost periphery of the volcanoes. 



The yellow tuff, like similar volcanic deposits, is invariably 

 stratified in very well-marked thin bands, coinciding with the 

 tectonic structure of the volcanic mass of which they form part. 

 This coincidence often helps the observer to reconstruct hypo- 

 thetically more than one volcanic edifice, which later cataclysms 

 have in part destroyed, or perhaps swept entirely away. The 

 layers, uniformly yellow, are sometimes intercalated with paler 

 grey bands, or, where they have been exposed to surface-alteration, 

 are sometimes covered with a sort of grey film. Asa rule, however, 

 the picturesque masses of yellow turf stand out from afar off, and 

 being fissured by vertical joints, form rugged and precipitous crags, 

 such as may be seen, for instance, below the Camaldoli and at the 

 headland of Posillipo. 



The eruptions of ash, lapilli, and pumice whence these masses of 

 yellow tuff, of an average thickness exceeding 300 feet, were 

 derived, were generally of an explosive character. But it seems 

 probable that lava-eruptions, though of rare occurrence, were not 

 entirely wanting ; and the products of such outbursts may well be 

 represented by the trachytic masses, met with in the tunnels of the 

 Cuman Railway and of the great Cloaca, which run beneath the 

 Yomero Hill. 



These eruptions, like those of the First Period (pipernoid tuff and 

 piperno), must also have taken place under the sea. This may 

 be inferred from the extreme and uniform compactness of the tuff, 

 and from the non-remanie or unaltered shells of Ostrea, Pecten, and 

 other marine organisms which occur sporadically buried in the tuff, 



On account of the great uniformity of this deposit, it does not 

 seem possible to map out any order of succession for the different 

 eruptive vents whence the materials of which it is built up were 

 derived. Geologically speaking, we may regard these eruptions as 

 contemporaneous manifestations of one great phase of vulcanicity 

 which affected the entire area of the Phlegraean Fields. 



It is true that some of the volcanoes built up of yellow tuff are 

 better preserved than others, some of which are barely recognizable. 

 But this greater or less degree of preservation is not due so much 

 ro difference of age, as to diversity of the accidents to which the 

 volcanoes have been subjected since their formation. Some of 

 them were sooner upheaved above the sea and to a higher altitude, 

 and were consequently exposed to longer and more destructive 

 atmospheric erosion. Several were broken up, or eviscerated, or 

 overwhelmed by later eruptions, while their neighbours escaped. 



