SI* Geological Societij. 



duced by the action of material things upon each other : and we 

 know that the laws by svhich 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 similar 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 forms 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 phasnomena exhibited by the fragments 

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

 grasp the means of a large induction : and our 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 phasnomena, 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 phaenomenaof 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 phaenomena recurring, again 

 and again, in a certain order ? I must confess that I cannot discover 

 even the traces of them ; and I think we do injustice to our subject, 

 in bringing it too nearly into comparison with the exacter sciences. 



The earth has been brought into its present form by countless 

 causes, of which we know nothing — by corpuscular and chemical ac- 

 tion, varied by changes of temperature, of pressure, and of all other 

 external conditions — by the violence of volcanic forces, called into 

 being by unknown powers of nature, and at unknown intervals of 

 time — by all the combined effects of mechanical degradation — and by 

 all the endless modifications of matter, resulting from beings possess- 

 ing the organs of life. These conditions are infinitely too complex 

 and ill defined to come within the grasp of any exact analysis. 



I believe 



