Geological Society. 5 1 



from, bear a strong analogy to existing species, the brown coal of 

 the Rhine is probably of the age of the lacustrine limestone of 

 Aix en Provence. 



Mr. Horner further throws new light upon the period of the tra- 

 chytic and basaltic eruptions of the Sieben-gebirge, which, like many 

 volcanic hills in central France, he supposes to have burst forth 

 from beneath an ancient lake j and whilst he indicates that this ridge 

 has been elevated posterior to the formation of the associated brown 

 coal, he shows that one of the lake-craters on the opposite bank of 

 the Rhine, the Rodderberg, was formed during a more recent period, 

 probably contemporaneous with the accumulation of the loess or loamy 

 alluvium. 



We are here naturally led to reflect upon that exciting theoretical 

 question concerning craters of elevation, which now divides the geo- 

 logists of France and Germany. In France, De Beaumont, Dufr6noy> 

 and others, contend for the establishment of the views of Von Buch 

 and Humboldt, which refer the crateriform cavities to simple expan- 

 sion of the earth's crust, caused by intumescence from within ; whilst 

 Cordier and Constant Prevost maintain that all these ancient cones 

 and craters present in their structure a direct analogy to the products 

 of modern volcanic agency, and have been similarly formed. 



M. Constant Prevost is preparing an account of his late voyage in 

 the Mediterranean, by which he hopes to convince us, that all the 

 most ancient geological phenomena, of igneous characters, can alone 

 be rationally explained by an appeal to existing evidences, thus har- 

 monizing in his speculative views with our countryman Mr. Lyell, 

 who, from an examination of the same districts, had before arrived 

 at similar conclusions, and who had been among the first to combat 

 the theory of elevation craters as applied to the Cantal and Mont 

 D'Or*. I must for a second time allude to the forthcoming volume of 

 this author, in which you will find descriptions of those interesting 

 tracts, the Eifel, and of Olot in Catalonia, coupled with an abun- 

 dance of striking and original observations respecting the volcanic 

 ejections of Etna, which absolutely demonstrate, that many of our 

 older trappsean currents must have had a similar origin. 



In concluding this review of works illustrative of volcanic pheno- 

 mena, I announce with delight that our secretary Dr. Turner, in co- 

 operation with Mr. De la Beche, has commenced a series of experi- 

 ments to determine the effects of heat upon various rocks, both crystal- 

 line and sedimentary, for thepurpose of elucidating the modes in which 

 some may have been formed, and others altered. The inquiry will after- 

 wards be extended to the production of simple minerals, and will also 

 lead to the repetition of some of the experiments of Sir J. Hall, in a 

 field nearly abandoned in Great Britain since his successful career, al- 

 though France and Germany have to boast of the important discoveries 

 of Berthier and of Mitscherlich. 



Having adverted to those works, of the past year, which may be con- 

 veniently classed under separate scientific heads, I will now briefly 



* Principles of Geology, vol. i. p. 386, &c. 

 H 2 



