2o8 CLASSICS OF MODERN SCIENCE 



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 ; secondly, those which govern the fluctu- 

 ation in the animate world ; and thirdly, the mode in which subter- 

 ranean movements afifect 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 survey 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 limestone 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 diatomacese. 



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

 sions of matter, it is exposed almost everywhere to waste away. For- 

 ests may be as dense and lofty as those of Brazil, and may swarm 

 with quadrupeds, birds, and insects, 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 innumerable bones and skeletons of birds, quadrupeds, and rep- 

 tiles, which tenanted the fertile region. Should this land be at length 

 submerged, the waves of the sea may wash away in a few hours the 

 scanty covering of mould, and it may merely import a darker shade of 

 colour to the next stratum of marl, sand, or other matter newly thrown 

 down. So also at the bottom of the ocean where no sediment is ac- 

 cumulating, seaweed, zoophytes, fish, and even shells, may multiply 

 for ages and decompose, leaving no vestige of their form or substance 

 behind. Their decay, in water, although more slow, is as certain and 

 eventually as complete as in the open air. Nor can they be perpet- 

 uated for indefinite periods in a fossil state, unless imbedded in some 

 matrix which is impervious to water, or which at least does not allow 

 a free percolation of that fluid, impregnated as it usually is, with a 



