PERMANENCY OF OCEAN-BASINS. 207 



materials found imbedded iii it. The mare clausum, with. 

 110 tides and perhaps but few large rivers flowing into it, 

 and its shores largely composed of hard crystalline rocks 

 like those of Scandinavia and the Ardennes, will, however, 

 to a certain extent remove this difficulty. Even then, 

 however, it is doubtful how sufficient material for the 

 formation of the chalk could have been obtained ; and 

 accordingly one of our most eminent living geologists 

 suggests that, in addition to its partially organic origin, 

 chalk may have been largely formed by a chemical pre- 

 cipitate of carbonate of lime. 



Be this as it may, the degradation of chalk from its 

 former position as a supposed typical abyssal deposit has 

 taught the great lesson that almost all the stratified rocks 

 with which we are acquainted were laid down in com- 

 paratively shallow water, and consequently has led to the 

 general acceptance of the grand doctrine of the permanence 

 of continents and ocean-basins. By this, of course, it is 

 not meant that the whole areas of several of our continents, 

 such as Europe, have not been (as we know they have), 

 many times over, beneath the sea. Indeed, what we have 

 already said as to the extent of what we may call the 

 cretaceous Mediterranean, shows that at a comparatively 

 late period of geological history a large part of central 

 Europe was sea. Neither does this doctrine forbid such 

 changes in the present configuration of the earth as would 

 be implied by a land connection between Africa and 

 southern India. What, however, it does say, and that in 

 the most emphatic manner, is that where continents now 

 are there deposits have always been going on, and there 

 land, of larger or smaller extent and of ever varying 

 contour, has always been ; while the great ocean-basins, 

 like those of the Atlantic and Pacific, have existed as such 

 since the globe emerged from its primeval chaos. This, 

 then, is the second great lesson taught by a lump of chalk ! 



We ha.ve, however, by 110 means yet exhausted the 

 interest connected with the subject of chalk. In the first 

 place, the gradually increasing marly character of the lower 

 chalk points to a condition when the sea was much less 

 deep than at the period of the white chalk. If, indeed, 



