CHAP. VI.] GEOGRAPHICAL AND GEOLOGICAL CHANGES. 83 



Animals did not create the lime which they secrete from the sea- 

 water, and therefore we have every reason to believe that the 

 inorganic sources which originally supplied it still keep up that 

 supply, though perhaps in diminished quantity. Again, the 

 great lime-secreters — corals — work in water of moderate depth, 

 that is, near land, while there is no proof whatever that there is 

 any considerable accumulation of limestone at the bottom of the 

 deep ocean. On the contrary, the fact ascertained by the 

 Challenger, that beyond a certain depth the " calcareous " ooze 

 ceases, and is replaced by red and grey clays, although the 

 calcareous organisms still abound in the surface waters of the 

 ocean, shows that the lime is dissolved again by the excess of 

 carbonic acid usually found at great depths, and its accumula- 

 tion thus prevented. As to the increase of limestones in recent 

 as compared with older formations, it may be readily explained 

 by two considerations : in the first place, the growth and de- 

 velopment of the land in longer and more complex shore lines 

 and the increase of sedimentary over volcanic formations may 

 have offered more stations favourable to the growth of coral, 

 while the solubility of limestone in rain-water renders the 

 destruction of such rocks more rapid than that of sandstones 

 and shales, and would thus lead to their comparative abundance 

 in later as compared with earlier formations. 



However weak we may consider the above-quoted arguments 

 against the permanence of oceans, the fact that these arguments 

 are so confidently and authoritatively put forward, renders it 

 advisable to show how many and what weighty considerations 

 can be adduced to justify the opposite belief, which is now 

 rapidly gaining ground among students of earth-history. 



Shore Deposits and Stratified Rocks. — If we go round the shores 

 of any of our continents we shall always find a considerable 

 belt of shallow water, meaning thereby water from 100 to 150 

 fathoms deep. The distance from the coast line at which such 

 depths are reached is seldom less than twenty miles, and is very 

 frequently more than a hundred, while in some cases such shallow 

 seas extend several hundred miles from existing continents. The 

 great depth of a thousand fathoms is often reached at thirty 

 miles from shore, but more frequently at about sixty or a hundred 



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