250 THE HISTORY OF GEOLOGY 



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 infinite. The mathematician often 

 employs in his calculations the device of assuming some 

 very large quantity to be infinite, and in this way obtains 

 approximate results sufficiently 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 6,000 years, but free to roam through the 

 ample magnitude of 30,000,000 ! It is at present impos- 

 sible to say how near the truth Lord Kelvin's estimate 

 may be ; it is founded on data which may be inexact, 

 and on assumptions which may be illegitimate, but that 

 it is approximately correct the preponderance of evidence 

 seems to show. 



That the strict uniformitarian view is as false in 

 philosophy as it is unfounded on fact is an opinion 

 which was shared by the late Professor Prestwich, and 

 which is held by many of the geologists of to-day, as 

 it was by the great masters of old. It is tantamount to 

 asserting that the progress of events on the earth can 

 be represented by a curve which is a straight line. We 

 should think strangely of the physicist who, from the 

 behaviour of a fluid through the range of ordinary atmo- 

 spheric temperature, should proceed to deduce from it 

 a rate of expansion up to the temperature of the sun 

 in one direction and down to absolute zero in the other ; 



