THE HISTORY OF GEOLOGY AT OXFORD. 47 



future, of which we know nothing, and scarcely in the past 

 itself, whose problems are to be explained. Epigrams are 

 frequently only a neat way of obscuring a truth, in this case the 

 fact would appear to be that most of the older observers, when 

 they encountered interruptions in the successionof strata, were 

 accustomed to explain them by interruptions in theorderly pro- 

 gress of nature, by sudden and violent changes, which were 

 spoken of as catastrophes. Hutton and Lyell were able to 

 offer explanations of these without the invocation of catastro- 

 phes. They certainly introduced the scientific method into 

 cases which had previously been treated by a too free use of 

 the imagination, and thus their doctrine, the doctrine of uni- 

 formity, has dominated geologic thought for the past sixty 

 years, and will probably continue to do so for many years 

 to come. The teachings of Hutton and Lyell have, how- 

 ever, another side ; they assume not only that existing 

 causes have acted in the past as in the present, but at the 

 same uniform rate : this was the natural result of a reaction, 

 which followed when Geology was loosened from her ancient 

 bondage to time, and under the influence of which geologists 

 came to regard the periods at their disposal as practically in- 

 finite. The mathematician often employs in his calculations 

 the device of assuming some very large quantity to be in- 

 finite, and in this way obtains approximate results suffi- 

 ciently close for working purposes. This is precisely what 

 Hutton and Lyell did in their explanations. But when a 

 limit becomes assignable to this quantity, the mathematician 

 will abandon the fiction of infinitude and introduce the 

 ascertained or estimated value into his equations with a 

 view to arriving at greater exactitude. Of late years it has 

 been asserted by a very high authority — Lord Kelvin — 

 that a limit can be assigned to geological time ; once more 

 Geology is put under bondage, not however, as in her youth, 

 tethered to a mere 6000 years, but free to roam through the 

 ample magnitude of 30,000,000 ! It is at present impossible 

 to say how near the truth Lord Kelvin's estimate may be ; 

 it is founded on data which may be inexact and on assump- 

 tions which may be illegitimate, but that it is approximately 

 correct the preponderance of evidence seems to show. 



