109 



the nodules of so-called Eozdon were simply concretionary under 

 inetamorphic rearrangements, and in a letter to Prof. H. J. 

 Johnston-Lavis, said, " I came away with the clear conviction 

 that we need no longer trouble about its organic nature."* 



The latest and most important contribution on this subject is a 

 joint paper read before the Royal Dublin Society by Prof. H. J. 

 Johnston and Dr. J. W. Gregory, and is published in the Trans- 

 actions of that Society for 1894.f The exhaustive observations 

 which the first-named of these authors has made on the geology 

 of Monte Somma brought to his notice some remarkable litholog- 

 ical features in certain ejectamenta from this old crater, and has 

 supplied the material for the joint paper now referred to, on the 

 " Eozoonal Structure of the Ejected Blocks of Monte Somma.' 

 The blocks in which this structure is seen were derived, according 

 to the authors of the paper, from limestones of Mesozoic age 

 situated at a considerable depth in the funnel of the volcano, and 

 the specimens show an intermediate degree of metamorphism 

 between the comparatively unaltered Tertiary beds in the upper 

 part of the sub-volcanic platform and the more completely fused 

 ultra-basic and basic rocks of greater depth. The genesis of this 

 eozoonal structure can be gathered from the examination of a 

 series of specimens in which it is more or less perfectly developed. 

 As the result of an examination of a large number of these 

 ejected fragments, the authors conclude that " the Eozoon struc- 

 ture has been produced in those limestones which have, under 

 great pressure, in the presence of different gases, and in the 

 neighbourhood of a comparatively basic magma, undergone whole 

 or partial fusion."! 



The remarkable concentric and laminar structure of the 

 eozoonal nodules is accounted for by the interaction of the lime- 

 stone and the more or less acid magma when brought into con- 

 tact. Along the line of contact a process of mutual modification 

 takes place. The limestone extracts a proportion of silica from 

 the magma, and the magma is rendered more basic, not only by 

 a loss of silica, but by the absorption of lime and magnesia from, 

 the limestones with which it is in contact. The so-called 

 " acervuline layer" in Eozoon is accounted for by this process of 

 interchange and chemical reaction, attenuated and irregular 

 silicate bands being produced by the exhaustion of the silicic 

 substances in penetrating into the limestone. The presence of 

 tubuli in Eozoon structure is the strong point of evidence with 



* " Eozoonal Structure of Ejected Blocks of Monte Somma," by Prof. H. 

 J. Johnston-Lavis and J. W. Gregory, D.Sc, Sc. Trans. Roy. Dublin Soc, 

 Vol. V. (Ser. 2), 1894, p. 274. 



t Op. cit. 



X Op. cit., p. 264. 



