UNIFORMITY OF CHANGE 421 



analogy of what is known both of the past and present 

 economy of our system. Although the discussion of so com- 

 prehensive a subject must carry the beginner far beyond his 

 depth, it will also, it is hoped, stimulate his curiosity, and 

 prepare him to read some elementary treatises on geology 

 with advantage, and teach him the bearing on that science 

 of the changes now in progress on the earth. At the same 

 time it may enable him the better to understand the inti- 

 mate connection between the Second and Third Bpoks 

 of this work, one of which is occupied with the changes 

 of the inorganic, the latter with those of the organic 

 creation. 



In pursuance, then, of the plan above proposed, I will 

 consider in this chapter, first, the laws which regulate the 

 denudation of strata and the deposition of sediment; second- 

 ly, those which govern the fluctuation in the animate world; 

 and thirdly, the mode in which subterranean movements 

 affect the earth's crust. 



Uniformity of change considered, first, in reference to 

 denudation and sedimentary deposition. First, in regard to 

 the laws governing the deposition of new strata. If we sur- 

 vey the surface of the globe, we immediately perceive that it 

 is divisible into areas of deposition and non-deposition; or, 

 in other words, at any given time there are spaces which are 

 the recipients, others which are not the recipients, of 

 sedimentary matter. No new strata, for example, are thrown 

 down on dry land, which remains the same from year to 

 year; whereas, in many parts of the bottom of seas and 

 lakes, mud, sand, and pebbles are annually spread out by 

 rivers and currents. There are also great masses of lime- 

 stone growing in some seas, chiefly composed of corals and 

 shells, or, as in the depths of the Atlantic, of chalky mud 

 made up of foraminifera and diatomaceae. 



As to the dry land, so far from being the receptacle of 

 fresh accessions of matter, it is exposed almost everywhere 

 to waste away. Forests may be as dense and lofty as those 

 of Brazil, and may swarm with quadrupeds, birds, and in- 

 sects, yet at the end of thousands of years one layer of black 

 mould a few inches thick may be the sole representative of 

 those myriads of trees, leaves, flowers, and fruits, those in- 



