UNDERGROUIfD PHENOMENA. 177 



Mallet, R. On some of the conditions influencing the Projection of 

 Discrete Solid Materials from Volcanoes, and ou the mode in 

 which Pompeii was overwhelmed. Journ. 2i. Geol. Soc. Ireland, 

 eer. 2, vol. iv. pt. 3, pp. 144-169 ; 3 plates. 

 Different volcanoes, or the same at different times, present two 

 distinct features. The erupted matter is in a state of fusion (lava), or 

 is comminuted solid material, ejected at temperatures below bright 

 incandescence and short of that of fusion. With the latter are also 

 thrown out masses and flakes of viscous lava. Such eruptive charac- 

 teristics have been for three centuries alternately displayed in the 

 eruptions of Vesuvius, as well as of Etna. A prevalence of discrete 

 incandescent ejecta is attributable to a comparatively low temperature 

 at the deeper volcanic /oct, or to a more infusible character of the beds 

 through which the volcanic ducts ascend, and may occur at the close of 

 eruptive paroxysms from diminution of local temperature. To such 

 ejecta from the crater of Vesuvius, carried S.E. by the wind, the author 

 ascribes the catastrophe of Pompeii, the dust being probably of a tem- 

 perature not higher than 250° or 300° F. On the other hand Hercu- 

 laneum appears to have been overwhelmed by solid discontinuous matter 

 at a high temperature, which rolled down the side of the mountain. In 

 neither case is there any evidence of the so-called illuviones or mud 

 eruptions, the mud that has been found in those cities being only the 

 result of the subsequent infiltration of water through the dry volcanic 

 dust. E. T. H. 



Mallet's Volcanic Theory " tested " by the Eev. 0. Fisher. 



Phil Mag. ser. 5, vol. i. pp. 19-22. 

 Mr. Fisher, in attempting to test the theory of volcanic energy by 

 mathematical reasoning (see Geological Eecord for 1875, p. 172), has 

 taken values for the coefficients of adhesion and friction which the 

 author assumed for illustration only, and he makes other unfounded 

 assumptions for the basis of his calculation. Until we know more of 

 the nature of the interior of the globe, the api)lication of mathematics 

 is likely to mislead. Special objection is taken to Mr. Fisher's alter- 

 native conclusion that part of the heat from the work of descent of the 

 crust is transformed into heat within the nucleus ; his own assumption 

 being that the nucleus is hotter than the heat of vulcanicity, (See 

 Fisher, p. 174.) F. D. 



. Formation of the Ocean-beds by Deformation of the Spheroid. 



Phil. Mag. scr. 5, vol. ii. pp. 61, 62. 



A note to guard against being supposed to agree with llev. 0. Fisher, 

 that it was unequal radial contraction that formed the ocean-beds. 

 Considers that our present knowledge does not enable us to fully explain 

 the deformation of the spheroid. F. D. 



Nordenskibld, Prof. A. E. Distant Transport of Volcanic Dust. 

 Discourse at the Annual Festival of the Swedish Academy of 

 1876. N 



