342 THE CAUSES OF THE n 



the real limitation of their inquiries, and to 

 forget the extreme imperfection of what is really 

 known. Geologists have imagined that they could 

 tell us what was going on at all parts of the 

 earth's surface during a given epoch ; they have 

 talked of this deposit being contemporaneous with 

 that deposit, until, from our little local histories of 

 the changes at limited spots of the earth's surface, 

 they have constructed a universal history of the 

 globe as full of wonders and portents as any other 

 story of antiquity. 



But what does this attempt to construct a 

 universal history of the globe imply ? It implies 

 that we shall not only have a precise knowledge of 

 the events which have occurred at any particular 

 point, but that we shall be able to say what events, 

 at any one spot, took place at the same time with 

 those at other spots. 



Let us see how far that is in the nature of 

 things practicable. Suppose that here I make 

 a section of the Lake of Killarney, and here the 

 section of another lake that of Loch Lomond 

 in Scotland for instance. The rivers that flow 

 into them are constantly carrying down deposits 

 of mud, and beds, or strata, are being as constantly 

 formed, one above the other, at the bottom of 

 those lakes. Now, there is not a shadow of doubt 

 that in these two lakes the lower beds are all 

 older than the upper there is no doubt about 

 that ; but what does this tell us about the age of 



