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Show 82 ISLAND LlFE. [PART I. find tho oceans, from which the sediments came to form the various deposits we now see. This view was held by so acute and learned a geologist as Sir Charles Lyell, who says:-" Continents therefore, although permanent for whole geological epochs, shift their positions ent~rely in the course of ages."1 Mr. T. Mellard Reade, late President of the Geological Society of Liverpool, so recently as 1878, says:-" While believing that the ocean-depths are of enormous age, it is impossible to resist other evidences that they have once been land. The very continuity of animal and vegetable life on the globe points to it. The molluscous fauna of the eastern coast of N ortb America is very similar to that of Europe, and thi~ could not have happened without littoral continuity, yet there are depths of 1,500 fathoms between these continents.''2 It is certainly strange that a geologist should not remember the recent and long-continued warm climates of the Arctic regions, and see that a connection of Northern Europe by Iceland with Greenland and Labrador over a sea far less than a thousand fathoms deep would furnish the "littoral continuity" required. Again, in the same pamphlet Mr. Reade says :-" It can be mathematically demonstrated that the whole, or nearly the whole, of the sea-botto1;11 has been at one time or other dry land. If it were not so, and the oscillations of the level of the land with respect to the sea were confined within limits near the present continents, the results would have been a gradual diminution instead . of development of the calcareous rocks. To state the case in common language, the calcareous portion of the rocks would have been washed out during the mutations, the destruction and re-deposit of the con tinental rocks, and eventually deposited in the depths of the immutable sea far from land. Immense beds of limestone would now exist at the bottom of the ocean, while the land would be composed of sandstones and argillaceous shales. The evidence of chemistry thus confirms the inductions drawn from the distribution of animal life upon theglobe." So far from this being a "mathematical demonstration 1 ' it appears to me to be a complete misinterpretation of the facts. 1 P1·inciples of Geology, 11th Ed., Vol. I.., p. ·258. :a On Limestone as an Index of Geological Time. CHAP. vi.] GEOGRAPHICAL AND GEOLOGICAL CHANGES. 83 Animals did not create the lime which they secrete from the seawater, 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 Challenge?·, 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 accumulation 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 development 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, "bile 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 \\.ith 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, a:p.d is vf;ry frequently more than a hundred, while in some cases such 2hallow 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 frequ~ntly at p,bo1.1t ~ixty or a hundred 0 2 |