112 GEOLOGICAL CHANGE, AND TIME. 



paced the stieettj amid which Ave are now gathered together; with them 

 he sought the crags and ravines around us, wherein Kature has hiid 

 open so many impressive records of her past; with tliem he sallied 

 forth on those memorable expeditions to distant parts of Scotland, 

 whence he returned laden with treasures from a field of observation 

 Avliich, though now so familiar, was then ahnost untrodden. The cen- 

 tenary of llutton's Theory of the Earth is an event in tlic annals of 

 science which seems most fittingly celebrated by a meeting of the 

 British Association in Edinburgh. 



In choosing from among the many subjects which might properly 

 engage your attention on the present occasion, I have thought that it 

 would not be inappropriate nor uninteresting to consider the more 

 salient features of that Theory, and to mark how much in certain 

 departments of inquiry has sx)rung from the fruitful teaching of its 

 autlior and his associates. 



It was a fundamental doctrine of Ilutton and his school that this 

 globe has not always worn the aspect which it bears at present; that 

 on the contrary, proofs may everywhere be culled that the land which 

 we now see has been formed out of the wrecli of an older land. Among 

 these proofs, the most obvious are supplied by some of the more 

 familiar kinds of rocks, which teach us that, though they are now por- 

 tions of the dry land, they were originally sheets of gravel, sand, and 

 mud, which had been worn from the face of long- vanished continents, 

 and after being spread out over the floor of the sea were consolidated 

 into compact stone, and were finally broken up and raised once more 

 to form part of the dry land. This cycle of change involved two great 

 systems of natural processes. On the one hand, men were taught that 

 by the action of running water tlie materials of the solid land are in a 

 state of continual decay and trans])ort to the ocean. On the other 

 hand, the ocean floor is liable from time to time to be upheaved by 

 some stupendous internal force akin to that Avhich gives rise to the 

 volcano and the earthquake. Ilutton further perceived that not only 

 had the consolidated materials been disrupted and elevated, but that 

 masses of molten rock had been thrust upward among them, and had 

 cooled and crystallized in large bodies of granite and other eruptive 

 rocks which form so prominent a feature on the earth's surface. 



It was a special 'characteristic of this philosophical system that it 

 sought in the changes now in progress on the earth's surface an ex- 

 planation of those which occurred in older times. Its founder refused 

 to invent causes or modes of oi)eration, for those with which he was 

 familiar seemed to him adeipiate to solve the i)roblems with whicli he 

 attemi)ted to deal. Xowhere was the profoundness of his insight more 

 astonishing than in the clear, definite way in wliich he i)roclaimed and 

 reiterated his doctrine, that every part of the surface of the continents, 

 from mountain top to seashore, is continually undergoing decay, and is 

 thus slowly travelling to the sea. Ue saw that no sooner will the «ea 



