RELATIONS TO OTHER SCIENCES 685 



work on the surface of the earth since the first precipitation of rain, 

 carbonic acid has been replacing silica from its bases; a large part 

 of the silica thus set free goes to form the hydrated variety of silica, 

 like opal, or ultimately free quartz. The bases are thus continually 

 being leached out of the emerged rocks of the continents, and car- 

 ried away to the ocean in solution, or in a colloid condition, the re- 

 sult being the ultimate deposition of the greater part of the heavier 

 materials in the abysmal regions of the ocean and an accumulation 

 of the lighter refractory quartz on or near the continental areas. 



A detailed study of marine deposits shows that, while quartz-sand 

 forms generally the largest part of the deposits close to the continents, 

 quartz-sand is, on the other hand, almost wholly absent from the 

 abysmal regions of the ocean far from land, except where the sea sur- 

 face is affected by icebergs. The average chemical composition of 

 terrigenous deposits near land and of continental rocks shows about 

 68 per cent of free and combined silica. On the other hand, the aver- 

 age chemical composition of abysmal deposits shows only 36 per cent 

 of silica. Continental rocks have an average specific gravity of 2.5. 

 The abysmal deposits now forming on the floor of the ocean would 

 make up rocks with a specific gravity of over 3.1. The superficial 

 layers of the earth's crust on the continents must be, therefore, con- 

 sidered specifically lighter than the superficial layers of the earth's 

 crust below the waters of the ocean. 



Everywhere along continental slopes and in inclosed seas we find a 

 series of strata being formed in all respects comparable with the strati- 

 fied rocks of the geological series. Glauconite is to be found now 

 forming on nearly all continental slopes, but it is not met with in the 

 deep-sea deposits far from land. This same mineral is found in the 

 same form as in recent deposits throughout the whole series of stratified 

 rocks from the pre-Cambrian down to the present time, so that it is le- 

 gitimate to assume that rocks in which it occurs were laid down close 

 to continental land. Phosphatic nodules are very intimately associ- 

 ated with glauconitic deposits, and have the same distribution in the 

 present seas; they are found along the submerged slopes of continental 

 land, and are very rarely met with in deep water far from continental 

 shores. There is a similar association of phosphatic nodules and glau- 

 conite throughout the whole geological series of past ages. These phos- 

 phatic and glauconitic rocks are now forming especially where ocean 

 currents from different sources and of different temperatures meet, as, 

 for instance, off the United States coasts in the Atlantic and Pacific, off 

 the Cape of Good Hope, off eastern Australia, off Patagonia, and off 

 Japan. In these areas there is a vast destruction of life, owing to sudden 

 changes of temperature of the sea-water. The organisms in the cold 

 current are killed from a sudden rise of temperature, the animals in 

 the warm current from a sudden lowering of the temperature. When 



