xiv PROCEEDINGS OF THE GEOLOGICAL sociETY. | May 1902, 
has largely influenced the evolution of ideas, but to trace this 
influence in detail is obviously impossible within the limits of an 
address like the present. All that I can do is to call attention to 
the more salient features, and to illustrate my remarks by a few 
examples of exceptional interest or importance. 
The great work on Chemical & Physical Geology by Gustav 
Bischof—the English translation of which appeared in 1854—marks 
an epoch in the history of our knowledge of the chemical and 
physical processes involved in the production of sedimentary rocks. 
It still remains a classic, for no writer since his time has combined 
the same knowledge of the facts of both chemistry and geology 
with the same powers of lucid exposition. He cannot, however, be 
regarded as a true prophet on all points, for in the preface to 
the English edition, after pointing out the necessity of further 
experimental research for the purpose of extending our knowledge 
of the processes concerned in the destruction, formation, and 
metamorphosis of rocks, he says :— 
‘The plutonic explanations, founded frequently on untenable hypotheses, 
will then retire more and more into the background, and at length vanish 
entirely out of science.’ 
But his pronounced neptunism detracts but little from the value of 
the work, for it is always possible to separate fact from theory, 
aud, so far at least as the sedimentary rocks are concerned, his 
neptunism is not altogether out of place. 
The striking feature of Bischof’s original work lies in the fact 
that it consisted very largely of experimental research suggested 
and controlled by an intimate knowledge of the facts of geology. 
He has had but few followers ; nevertheless it is satisfactory to 
note that during recent years there has been a tendency to return 
to his methods. ‘This is seen in such researches as those of Murray 
& Irvine ‘On the Chemical Changes which take place in the 
Composition of the Sea-Water associated with Blue Muds on the 
Floor of the Ocean’! and ‘On the Manganese-Oxides & Manganese- 
Nodules in Marine Deposits’’?; of Van ’t Hoff and his students on 
the conditions under which the Stassfurt salts were deposited ; and 
of various Russian observers’ on the chemical, physical, and physio- 
logical processes involved in the formation of the deposits of the 
1 Trans. Roy. Soc. Edin. vol. xxxvii (1893) p. 481. 
2 Ibid. vol. xxxvii (1894) p. 721. : 
* Guide des Excursions du VII&™* Congrés Géologique International (1897) : 
No. xxix, ‘La Mer Noire’ by Prof. N. Andrussov. 
