VII.] ON SOME POINTS IN DYNAMICAL GEOLOGY. 79 



Moreover, these strata already include, not only water, but 

 the compounds of chlorine, sulphur, and carbon necessary for 

 the generation of the various gases which are the frequent ac- 

 companiments of volcanic eruptions.* With the contributions 

 of Vose and Mallet, the theory of volcanic action advocated by 

 Keferstein, Herschel and myself would seem to be wellnigh 

 complete. 



* That the view so fully set forth in papers I. and II. of the present vol- 

 ume, in the years 1858 and 1859, as to the origin of volcanic products, is the 

 one now adopted by Mallet, appears from the following extract of a letter 

 by him in Nature, for March 20, 1873 : " There is just that general similarity 

 in the constitution of volcanic products which we should expect to result 

 from the heating or the fusion together of the beds, more or less silicious, 

 aluminous, magnesian, or calcareous, mixed with metallic oxides or other 

 compounds, and often with carbon, boron, and other elements, all variously 

 superposed or mixed, which constitute the known crust of the earth." 



