146 T. Mellard Reade—The Age of the World. 



world was enormously greater than any one had before contem- 

 plated. 



So averse, however, is the human mind to receive new impres- 

 sions, that the first geologists had to shorten the life of the world 

 by periodical convulsions and the assumption of more potent 

 natural causes in the earlier periods of the Earth's history. 



In this again they were assisted by another vice of the mind — 

 that of generalizing from small data. Faults, foldings of the strata, 

 and other evidences of former volcanic activity, that have been 

 since proved to be only local phenomena, were assumed to have 

 extended all over the Earth at the same time, and to have separated 

 its history into " periods." This I call constructive geology, due to 

 an unscientific use of the imagination. Yet those crude and hasty 

 generalizations were not to be wondered at; for the peculiar scientific 

 habit of thought engendered by sound geological reasoning had not 

 then been acquired. 



To Hutton is due the merit of placing geological investigation on 

 a sound basis, and to Lyell philosophical geology almost owes its 

 existence. 



The conception of the possibility of explaining all the phenomena 

 of the Earth's crust by agencies at present at work, lies at the 

 foundation of all geological reasoning. It is one, however, that does 

 not necessarily commend itself to the judgment at first sight, 

 because there are no a-priori improbabilities in conceiving that 

 agencies may have been at work at former periods of which we 

 now know nothing. If, however, we attentively study the Earth's 

 crust, we become gradually convinced that the agencies we are 

 acquainted with are competent to explain all the complicated phe- 

 nomena with which it abounds, and not only so, but that no other 

 agencies can satisfactorily explain them. 



Therefore, instead of a playful exercise of fancy, we begin our 

 investigations on a sure foundation — so sure indeed that no geologist, 

 so far as I am aware, has been compelled to adopt any other hypo- 

 thesis, though of course different opinions are held with regard to 

 the relative activity of these forces at various stages of the history of 

 the Earth. 



Geology, then, is a pre-eminently practical common-sense science, 

 because it is always testing its conclusions by reference to the Earth 

 itself. The reasoning is essentially of an inductive cast. It is 

 necessarily a safe science, for it cannot get far on the wrong road 

 without being set right. Astronomy is a more exact science ; the 

 relations it sets itself to investigate are simple ones — mechanical 

 conceptions capable of mathematical demonstration and verification 

 by exact measurement. When I say the relations it investigates 

 are simple, I say it with the profoundest respect ; for the solutions of 

 some of these problems are among the greatest triumphs of the 

 human mind. The method of procedure is, however, essentially 

 different, and the attempt to displace the geological by the me- 

 chanical method in developing the geological history of the Earth 

 is, I trust to be able to show, one not likely to succeed. 



