214 GLIMPSES OF NATURE. 



upon the world frost, ice, snow, internal heat, animals 

 and plants, water, and atmosphere he declares, with 

 reason, are exactly those which have always been at 

 work moulding and sculpturing the earth's crust. 

 Rivers and seas and glaciers, volcanoes, and earth- 

 quakes, act to-day as they have always worked in the 

 past. The differences in their work have been merely 

 those of degree and not of kind ; and thus postulating 

 the uniform way of the world (in a geological sense) he 

 proceeds to reason about its past from his observation 

 of its present affairs. 



Our quarry's history becomes clear enough in the 

 light of this reasoning. Where, to-day, do we find 

 any approach in nature to the making of a quarry ? 

 The geologist says, you see such evidence chiefly in 

 the case of lakes, and also, to some extent, it may be, 

 on the shores of shallow seas. Think of your lake 

 for a moment. Into it run rivers, bringing the debris 

 they have worn and stolen from the land. This wear 

 and tear consists of sand, mud, gravel, and like 

 material. It is all deposited in the bed of the lake, 

 and it tends moreover to arrange itself in a given 

 order. The heavier matters sink lowest; the lighter 

 sand and mud lie on the top. 



There is thus a tendency to arrangement of material 

 seen from the first in the case of the lake-bed. Now, 

 extend your glance, by a scientific use of the imagi- 

 nation, forwards through a good few centuries. The 

 old lake is being gradually filled up by its river-debris, 

 and its further history is one of choking and extinction 

 in so far as its lake-character is concerned. The lake 

 is now a swamp or morass. Its rivers flow through, 

 over, and above the spot into which they were once 

 accustomed to pour their waters. 



