THE 



GEOLOGICAL MAGAZINE. 



No. XLV.— MARCH, 1868. 



<D:ElX<3rXlSTJ^Xj .^I^TIOXJES. 



I. — On Dr. Sterry Hunt's Geological Chemistry. 

 By David Forbes, F.E.S. 



IN considering the mutual relations of the sciences of Geology and 

 Chemistry, the student must always bear in mind which of 

 these two sciences is to form the basis or starting point for his 

 inquiry, for this cannot fail to exercise an important influence on his 

 reasonings and deductions. 



In what Dr. Sterry Hunt calls my Chemical Geology,^ I have taken 

 Geology as my starting point, and then endeavoured to apply che- 

 mistry, especially experimental chemistry, to the explanation of 

 known geological phenomena. On the other hand. Dr. Hunt, in 

 what may be termed his Geological Chemistry, starts from data purely 

 chemical, and then looks around for geological instances to which 

 they may be applied. 



Thus, for example, starting from the chemical fact, that a 

 solution of carbonate of soda will throw down carbonate of lime 

 from a solution of the chloride of calcium, he at once asserts 

 that the whole of " the calcareous strata, the marbles and various 

 limestones which we find on the earth's surface," have been precipi- 

 tated from the sea by a solution of carbonate of soda. 



And again, Dr. Hunt observing in the laboratory that the reaction 

 of the compounds of magnesia with carbonic acid in a dense atmo- 

 sphere of that acid could be turned to account in facilitating the 

 separation of Dolomites and Gypsums, at once jumps at the conclu- 

 sion " that all magnesian limestones and gypseous strata from the 

 most ancient up to the Tertiary periods were formed in a dense atmo- 

 sphere of carbonic acid." Now in face of these assumptions, I con- 

 tend and I feel confident the Geological world will bear me out, that 



^ Here it should be explained that Dr. Hunt, from having some time back published 

 both in England and France an outline of his principles of Chemical Geology, has 

 thereby fairly laid himself open to having his views both criticised and disputed ; 

 whilst, on the contrary, Dr. Hunt's knowledge of my views on this subject could be 

 only derived from the allusions to my opinions scattered through the two papers re- 

 lating to this controversy in the Geological Magazine of October 1 and the Chemical 

 News of October 4 of last year. Although his virulent criticism might therefore be 

 considered as hardly fair; still, so far from objecting to it, I feel truly thankful to Dr. 

 Hunt for thus enabling me to strengthen the weak points, and inspiring me with more 

 confidence than before in the resume of the views on Chemical Geology put forth in a 

 lecture to the Chemical Society, now in the press. 



VOL. V. — NO. XLV. 8 



