Masterpieces of Science 



face 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 mat- 

 ter. 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 bot- 

 tom 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 dia- 

 tomaceas. 



As to the dry land, so far from being the recep- 

 tacle 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 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 reptiles, 

 which tenanted the fertile region. Should this 

 land be at length submerged, the waves of the sea 

 way wash away in a few hours the scanty cover- 

 ing of mould, and it may merely impart 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 sedi- 

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