[ «7 ] 



GEOLOGICAL SOCIETY OF DUBLIN. 



March 11, 1846. — On some Secular and Diurnal Motions of the 

 Earth's Crust, &c. By Robert Mallet, Esq., Mem. Ins. C.E., 

 M.R.I.A., President of the Society. 



The President said, that on taking the chair for the first time, he 

 could not better mark his sense of the great honour which the So- 

 ciety had conferred on him in electing him their President, than by 

 laying before them a plan which he had for some time conceived for 

 the organization and carrying out of arrangements for a great, com- 

 bined, and comprehensive movement for the promotion of a parti- 

 cular branch of geological discovery. 



Geology might be divided into topographical and physical, both of 

 which require for their study and development, the confluent aid of 

 several distinct branches of natural inductive science, as well as of 

 the exact sciences properly so called. Physical geology, again, might 

 be divided into several distinct branches, for the cultivation of all of 

 which, the application of physics, mechanics, and chemistry, in 

 their largest senses, is indispensable. For a considerable period it 

 had aj^peared to him that one of the most important directions in 

 which physical geology could be advanced was, in placing it in con- 

 nexion with a mode of investigation, new as respected geology, 

 although old as regarded other sciences, namely, measurement ; by 

 the organization and solution of such questions as were capable, in 

 terrestrial physics, of having an answer in measure, number or weight. 

 The application of measures to geology might be called experi- 

 mental geology — a brapch of the science hitherto, he might say, 

 unexplored. Geologists had hitherto contented themselves with 

 observing what nature had presented to them, and that must, from 

 the nature of geology, at all times form the staple of its investiga- 

 tions ; nevertheless, whenever it was possible to use the experimen- 

 tal method, it might be pronounced not only as the most certain, but 

 also the most rapid means of advancing geological, as it had always 

 been of every other branch of physical science. In order to illus- 

 trate what he meant by measurement in geology, and to show its 

 feasibility, and even simplicity of application, and to what import- 

 ant consequences it at once led, he would briefly give an example of 

 the sort of inquiry alluded to. Taking any large island, such as 

 Ireland, let them suppose the following data respecting it to be ob- 

 tained in measures — the entire amount of water annually discharged 

 into the sea by all its rivers, and the entire amount of soluble and 

 suspended matter carried down to the sea by them, and the chemical 

 constitution of these. From these data they should be able to pro- 

 nounce on the amount and on the character of deposits annually 

 taking place round the coasts. They should then be in a condition, 

 with the assistance of their tidal and other knowledge, to predicate 

 with a considerable degree of accuracy the nature, character, extent, 

 form, and relative locality, of the deposits so taking place ; and hence 

 to predict what forms of rock would at a future period be most 

 likely to occur round their shores ; to draw direct conclusions from 



F2 



