416 Proceedings of the Royal Society of Edinburgh. 



might be expected ; and this dubious character, which U particU' 

 larly remarked in the hill of Gergovia, near Clermont, forms an 

 admirable parallel to some cases in trap districts where a like want 

 of alteration occurs. 



The mineral character of the rocks of Auvergne admits of al- 

 most perfect identification in a majority of cases with that of un- 

 doubted trap-rocks ; and we may employ the formations of Central 

 France as a medium of comparison between trap-rocks generally, 

 and modern volcanos, from which the formations of the Mont- 

 Dome are undistinguishable. The trachytes of the Mont Dor and 

 Cantal find their counterparts in the districts of the Siebengebirge 

 and Laacher-See. Various points of structure were noticed as 

 important, especially the columnar forms of lavas, geologically 

 speaking, modern, which has been often referred to ; and more re- 

 markably the union of the tabular, with the polygonal columnar 

 structure, exhibited in the undoubtedly igneous trachytes, basalts, 

 and phonolites of the Mont Dor, which are sometimes so exten- 

 sively slaty as almost to assume the appearance of stratified rocks. 

 The very remarkable passage of one rock into another differing in 

 mineral chai'acter and structure was also pointed out, and hence 

 the difficulty of pronouncing conclusively upon the relative age of 

 such rocks. 



The second part of the paper referred to Von Buch's Theory of 

 Elevation- Craters, and professed to give simply the impression 

 made upon the author's mind by an examination of the specific 

 cases of the groups of the Cantal and Mont Dor, which have been 

 quoted as examples in support of that theory. Various views of the 

 subject were presented, from which the author is disposed to con- 

 clude decidedly in favour of the Elevation Theory in these particular 

 cases. The arguments were drawn chiefly from the forms and 

 magnitude of the valleys, and the relation of the beds of igneous 

 rock to one another, in which the valleys are formed. The author 

 expresses some doubt as to the utility of the calculations entered 

 into with regard to this question by MM. Elie de Beaumount and 

 Dufrenoy, and especially as regards the complicated system of the 

 Mont Dor, of which he considers it almost hopeless to unravel the 

 manifold revolutions. In general, however, he coincides in the 

 conclusions arrived at by those authors. 



2. Notice of a New Compound of Sulphur, which is probably 



a Sulphuret of Nitrogen. By Dr Gregory. 



3. On another New Compound of Sulphur, analogous to the 



Mercaptan of Zeise. By the same. 



4. On a curious Phenomenon observed in the Island of Ce- 



phalonia, and on the proximate cause of Earthquakes in 

 the Ionian Islands. By Dr John Davy. 



