Vol. 58. | ANNIVERSARY ADDRESS OF THE PRESIDENT. lxiik 
THE EVOLUTION OF PETROLOGICAL IDEAS. 
Last year I selected as the subject of my address the evolution of 
petrological ideas during the nineteenth century, but considerations 
of time and space obliged me to confine my remarks to the igneous 
rocks. On the present occasion I propose to continue the subject, 
by treating of the sedimentary rocks and the crystalline schists 
from the same point of view. 
The numerous and exacting duties which have devolved upon me 
in consequence of the change in my position have prevented me 
from giving that attention to the subject which its importance 
demands, and I have therefore to ask for your indulgence. What I 
have to offer to you must be regarded only as a brief and imperfect. 
sketch. 
Let us consider, first of all, the 
SEDIMENTARY Rocks. 
The resemblance of many of the stratified rocks to the deposits 
formed in rivers, lakes, and seas was recognized at the beginning 
of the century ; and the true principles by which their origin can 
be explained were clearly realized by Hutton and Playfair; but so 
long as the catastrophic theory of Cuvier and others dominated the 
world of geological thought, any great advance was impossible. 
The first volume of Lyell’s ‘ Principles’ appeared in 1830, the second 
in 1832, the third in 18338, and from that time onward the idea 
that observed facts, so far at least as the sedimentary rocks are 
concerned, must be explained by causes now in operation has 
influenced geological research and controlled geological thought in 
this country. The same idea spread more slowly in Germany, 
where its progress was retarded by the influence of Von Humboldt 
and Von Buch, and still more slowly in France, where the catas- 
trophic theory of Cuvier was supported by Elie de Beaumont and 
Alcide d’Orbigny. But it finally prevailed, and the growth of our 
knowledge with regard to the sedimentary rocks became slow and 
sure. So far as we are in a better position than our ancestors, this 
is due to the fact that we have more knowledge of the chemical, 
physical, and organic processes involved ; a deeper insight into the 
nature of the rocks themselves; and a better acquaintance with the 
deposits now in course of formation. 
The growth of knowledge in each of these three departments 
