340 EEPORT— 1892. 



shows more or less nnconformability, which corresponds as they themselves 

 do with those beds of the Monte Santo Funicular Railway, the Cumana Rail- 

 way, Pianura, Soccavo, Monte di Procida, Nocera, Castellamare, St. 

 Agata, Capri, Caserta, &c., which I have described in other reports and 

 papers. 



These are the principal sections which record the later geological 

 history of the Phlegrsean Fields, and from which I have been able to un- 

 ravel the stratigraphy of the highly complex Neapolitan volcanic region. 

 So far it has been explained only in these reports and other disjointed 

 papers, but before long I hope to be able to place before the scientific 

 world a far more detailed description of one of the most interesting as 

 well as the most classic and accessible volcanic regions of the world. 



Before quitting the subject, however, I wish to call attention to the 

 confirmation that the sections mentioned in this report aS'ord of my 

 explanation of the piperno and pipernoid structure in general. We see 

 distinctly that the variation in colour and texture of the two constituents 

 of the piperno, which chemically are identical, is simply due to the greater 

 saturation with H2O of one portion of the magma than the other in the 

 old chimney of the volcano at the time of the eruption. The consequence 

 was that the more aquiferous part was erupted as a fine dust, and the 

 less aquiferous, more coherent magma was ejected in large fragments or 

 more or less scoriaceous cakes, which lost their heat the more slowly, the 

 less H2O contained in them there was to expand. The densest, and at the 

 same time the slowest to cool, fell near the eruptive mouth, flattened out, 

 squeezed out those beneath them, and were squeezed out by those above 

 them, forming, with the included dust, the compact piperno in which the 

 foliated structure is most developed towards the W. end of the Soccavo 

 section, where the nearest existing remnant to the old ci-ater is now pre- 

 served, and where the inclination was greatest, and consequently where 

 actually slight flow took place. The more scoriaceous of these lava 

 cakes were carried to greater distances, so that as we travel away from 

 the eruptive axis we find, first, that the black fragments become less 

 markedly flattened because they cooled more rapidly from expansion, and 

 also because they travelled farther, until they no longer show flattening 

 parallel to the bedding more than what would be due to any of them 

 being accidentally of flattened or elongated form, and so lying flat on the 

 surface on which they fell ; second, we find that as their radial distance 

 from the eruptive axis increased, the fragments at first get lighter ; and 

 third, when the limit of lightness and cohesion is reached, they get 

 smaller and smaller, so that at Roccamonfina and Salerno the pipernoid 

 tulFis chiefly composed of the grey dust with only few and minute frag- 

 ments of black scorias. This seems to have been modified by strong winds, 

 and possibly by the eruption taking place along a cleft much like that 

 formed in the late Tarawera eruption, or as in many cases in Iceland, 

 such as the Skaptar outburst, though most of the latter locality do not 

 belong to explosive types of eruptions. 



There is in Iceland, at Krisuvik, the principal one of several crater 

 lakes which exhibits in a striking manner the resoldering together of 

 ejected fragments, into what might at first appear to be a true lava stream. 

 I allude to the Groenavatn, in which we have an almost circular conical 

 hollow nearly filled with water. There is only a very low ring around it, 

 composed of accidental ejectamenta, being nothing more than the ejected 

 fragments of the materials, through which it was drilled, with practically 



