211 



Are we then for ever to wander among the mere perplexities of 

 details, and never to hope for any system by which we may com- 

 bine them ? You must have seen, Gentlemen, that I am not the ad- 

 vocate of any such steril sentiment. It is indeed true that in the 

 very classification of our facts and of our phenomena, there are 

 difficulties connected with all parts of natural history, which, for 

 ages yet to come, may continue to require for their solution a com- 

 bination of the greatest industry with the greatest skill. But these 

 difficulties do honour to our science : and the same great rule by 

 which the father of physical astronomy was guided, applies, at 

 every step, to us and to our conclusions. " Effectuum naturalium 

 ejusdem generis esedem sunt causae," was the grand rule of his in- 

 duction. In the same way, we see the effects produced by the ac- 

 tion of material things upon each other : and we know that the laws 

 by which these material things are governed, are liable neither to 

 change nor intermission. There is, therefore, one safe rule in all 

 our inquiries, whether they be simple or complicated. Effects si- 

 milar in kind to those which are produced now, must in all former 

 times have been produced by some corresponding power of nature. 



As the historians of the natural world, we can describe the order 

 of the events which are past ; and we can trace a succession of re- 

 volutions through which we go back, till we arrive at periods where 

 the characters of nature's work are all obliterated, and there our 

 descriptions end. Like things we can compare with like ; and this 

 comparison teaches us the analogies of the fonns which we exa- 

 mine : but we define not the length of time during which they were 

 elaborated ; and still less do we dare to speculate about the physical 

 revolutions of the ages which are to come. 



The very commencement of the task of speculative geology re- 

 quires a wide and philosophic knowledge of the physical world as it 

 now is, and of all the great phenomena exhibited by the fragments 

 of its former history. A mind so prepared has already within its 

 grasp the means of a large induction : and bur science, though hardly 

 yet come out of its cradle, has supplied materials of thought for in- 

 tellects the most robust, and results to satisfy imaginations the most 

 ardent. Let us, therefore, go on as we have begun ; giving up our 

 best efforts to the search of new facts and of new phsenomena, and 

 using them like men who have no higher passion than the love of 

 truth. 



The greatest problems of astronomy are simple in their conditions. 

 A few physical points moving in free space, with given velocities, in 

 given directions, and acting upon each other in subordination to a 

 given law, — these constitute the chief data for the mathematical analysis 

 of the system of the heavens. And the results are of a corresponding 

 simplicity. The phsenomena of the heavens are demonstratively proved 

 to recur in a fixed order, after the lapse of fixed periods of time ; and 

 the apparent aberrations from the general law are also proved to be but 

 modifications of that law, and to return into themselves after the com- 

 pletion of definite secular periods. But where are the secular periods 

 of geology, and where are its cycles of phsenomena recurring, again 



