RELATIONS TO OTHER SCIENCES 687 



deposits are being formed on the floor of the ocean, the only varying 

 condition being depth. The calcareous organisms are all dissolved 

 away in falling through an ocean 20,000 feet in depth, or soon after 

 they reach the bottom, whereas they nearly all reach the bottom at 

 a depth of 5000 or 6000 feet, and there accumulate so as to form an 

 almost pure deposit of carbonate of lime. The clayey deposit at 

 20,000 feet evidently accumulates with extreme slowness, the calca- 

 reous deposit at 6000 feet much more rapidly. The recent observa- 

 tions of telegraph engineers appear to show that, at one place in the 

 North Atlantic, Globigerina ooze forms at the rate of about one inch 

 in ten years. 1 In the case of terrigenous, as well as of pelagic de- 

 posits, it has been shown that two very different deposits, both in 

 organic and inorganic constituents, may be formed in the same 

 area at the same time, but in different depths. 



All these considerations go to show that the deposits formed in 

 inclosed seas and along the borders and slopes of emerged contin- 

 ental land have again and again been shoved up on the continental 

 areas to form dry land, by the action of those internal forces called 

 into play through the solid crust accommodating itself to a shrinking 

 nucleus. And, further, it follows that more than one half of the sur- 

 face of the planet the abysmal regions of the great ocean basins 

 may never have contributed to the formation of those stratified 

 rocks of which continental land is so largely made up. The continents 

 have been far from permanent and stable, but those areas on the sur- 

 face of the planet now occupied by the continents and the adjacent 

 marine terrigenous deposits appear, from the foregoing argument, 

 to have been the areas on the surface of the planet on which con- 

 tinental land has been situated from the very earliest ages. The 

 grand result of all the denuding and reconstructing agencies since the 

 first precipitation of rain has been the building-up on these contin- 

 ental areas of a great mass of lighter highly siliceous materials. If 

 this has been the course of the evolution of the present continental 

 areas, then it appears amply to account for the deficiency of matter 

 beneath the continents indicated by pendulum observations, and for 

 the alleged fact that along continental shores the plumb-line tends 

 towards the ocean basins, where the heavier materials have been 

 accumulating on the earth's surface, ever since the first precipitation 

 of water on the cooling crust. 



Temperature may be defined as that state of matter on which de- 

 pends its relative readiness to give or to receive heat. Variations of 

 temperature are intimately associated with all changes in nature, and 

 nowhere are the effects of these variations of temperature more pro- 



1 See Murray and Peake, On Recent Contributions to Our Knowkdge of the Floor 

 of the North Atlantic Ocean, Roy. Geogr. Soc., Extra Publication, It 04, p. 21. 



