510 Notices of Me.ijwirs — Dr. Jolmdon-Lavis on Vesnvim. 



Soccavo section, where the nearest existing remnant to the old crater 

 is now preserved, and where the inclination was greatest, and con- 

 sequently 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 a flattened 

 or elongated form, and so lying flat on the surface they fell upon ; 

 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 tuff is 

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

 ments of black scoriae. 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 outbui'st, though most of the latter 

 locality does not belong to explosive types of eruptions. 



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

 crater lakes that exhibit 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 round it, composed of accidental ejectamenta, 

 being nothing more than tlie ejected fragments of the materials, 

 through which it was drilled, with practically no essential ejecta, 

 except on one side, where we have a mass of rock that looks like a 

 lava stream. It seems there must have been at the moment of the 

 eruption a very strong wind which carried all the lava fragments 

 in one direction, and as they fell they blended together into one fairly 

 uniform mass, the components of which are only faintly indicated 

 by a slight variation in colour, somewhat like piperno, but not so 

 well marked. The top and bottom ai'e less coherent, for at the 

 bottom the fragments fell on cold ground, whilst the top, although 

 falling on the hot mass beneath, could not be pressed into contact 

 with it by later falls. No doubt also the explosions were feebler 

 towards the end and the interval longer between the fall of the last 

 fragments. 



We find exactly the same thing in the piperno, namely, a spongy 

 tufaceous-like bottom and top. Besides this, the lulls and accen- 

 tuations of the explosive action are well marked, as well as the time 

 that large masses of the crater edges fell in and were re-ejected. 

 At one time the eruptive action seems to have been arrested, and the 

 partly or entirely consolidated plug was blown out into fragments 

 and deposited amongst the piperno. 



Vesuvius has since the last report, up to the time of my last visit 

 in May, shown very little variation. It will be remembered that 

 lava was issuing at the site of the eruption of June 7, 1891, at the 



