Correspondence — Dr. H. J. Johnston-Lavis. 143 



witli the skeleton of a prehistoric man, probably of Neolithic age, in 

 a cave at Mentone.^ 



There are some interesting notes by Dr. Robert Brown, F.L.S., 

 F.R.Gr.S. (1868), and Mr. Alexander C. Anderson (Yancouver Island) 

 on shells used by prehistoric people and modern North American 

 Indians as ornaments (see Heliqtiice Aquitanicce, by E. Lartet and 

 H. Christy, edited by T. Rupert Jones, 1865-75, p. 296). In the 

 same work also at p. 70 a shell-necklace from Cro-Magnon Ca%'e is 

 figured on B, pi. xi, co-mposed of Littorina liUorea, Purpura lapilliis, 

 Turritella communis, etc. 



In tlie Cavern of Bruniquel explored by the Vicomte de Lastic in 

 the Valley of the Aveyron fossil shells were found perforated, which 

 had evidently been used as personal ornaments (see op. cit., p. 70) ; 

 the collection is now preserved in the British Museum. 



^_^ H. W. 



SEA-WATEE AND CEITICAL TEMPEEATUEES. 



SiE,, — How very true the parable of the moat and the beam is, and 

 what a good example thereof is afforded by the letter of Mr. A. R. 

 Hunt in your last number ! He accuses his fellow- workers in geology, 

 after a disquisition on the knowledge of foreign languages, of 

 neglecting the researches of Daubree and othei- workers abroad. Yet, 

 although he has written on the subject of sea-water in volcanic and 

 metamorphic action, he has apparently never read some dozen or more 

 papers of mine on that subject, written years before (1892-4), though 

 his own countryman. 



I have distinctly shown that the critical point of water has nothing 

 whatever to do with the question, and that we have to consider the 

 physical conditions of the gas Hg in solution, under varying pressure 

 in fused silicates and oxides. I have urged the alkalinization of 

 magmas by the assimilation of the alkaline salts in sea and other 

 water, and accompanied by the liberation of the acid radicles in the 

 form of the enormous emanations at volcanic vents. Furthermore, as 

 mineralizers and fluxes, I have mentioned over and over again saline 

 substances as being great agents in metamorphism. I laid down the 

 fundamental principles of eruptive activity, which have never been 

 controverted or controvertible because they are demonstrated and 

 illustrated in all volcanic regions, principally by the nature and 

 characters of the fraj!;mentary ejecta of volcanoes. 



Strangely enough, geologists and petrographers steadily and 

 uniformly ignore the invaluable lessons taught by a study of 

 fragmentary ejecta, while they cover thousands of pages with 

 hypothetical, chemical groupings of massive rocks, ornamented by 

 the most astoundingly complicated nomenclature, which, in the end, 

 adds naught to our knowledge. Almost equally uselessly, they make 

 elaborate calculations of percentages of different hypothetical felspars, 

 and are blind to other structures that really record the vicissitudes 

 between the primitive, purely vitreous paste and the consolidated rock. 



^ See Comptes Rendus, No. 26, p. 1597, June, 1872 ; also Geol. Mag., 

 Vol. IX, pp. 272-4, 1872 (with a figure) ; also op. cit., p. 368, and article by 

 Professor John Morris, Pop. Sci. Review, July, 1872. 



