ERA OF THE PRIMARY ROCKS. 



29 



ties at the bottom of that sea, the heat rises up to what 

 was formerly the surface ; and when a second quantity of 

 sediment is laid down, it continues to rise through the 

 first of the deposits, which then becomes subjected 

 to those changes which heat is calculated to produce. 

 This process is precisely the same as that of putting ad- 

 ditional coats upon our own bodies ; when, of course, the 

 internal heat rises through each coat in succession, and 

 the third (supposing there is a fourth above it) becomes 

 as warm as perhaps the first originally was. 



In speaking of sedimentary rocks, we may be said to be 

 anticipating. It is necessary, first, to show how such 

 rocks were formed, or how stratification commenced. 



Geology tells us as plainly as possible that the original 

 crystalline mass was not a perfectly smooth ball, with air 

 and water playing round it. There were vast irregulari- 

 ties in the surface — irregularities trifling, perhaps, com- 

 pared with the whole bulk of the globe, but assuredly vast 

 in comparison with any which now exist upon it. These 

 irregularities might be occasioned by inequalities in the 

 cooling of the substance, or by accidental and local slug- 

 gishness of the materials, or by local effects of the con- 

 centrated internal heat. From whatever cause they arose, 

 there they were, enormous granitic mountains, intespersed 

 with seas which sunk to a depth equally profound, and 

 by which, perhaps, the mountains were wholly or par- 

 tially covered. Now, it is a fact of which the very first 

 principles of geology assure us, that the solids of the globe 

 cannot for a moment be exposed to water, or to the atmos- 

 phere, without becoming liable to change. They instantly 

 begin to wear down. This operation, we maybe assured, 

 proceeded with as much certainty in the earliest ages of 

 our earth's history, as it does now, but upon a much more 

 magnificent scale. There is the clearest evidence that the 

 seas of those days were not in some instances less than' a 

 hundred miles in depth, however much more. The sub- 

 aqueous mountains must necessarily have been of at least 

 equal magnitude. The system of disintegration consequent 

 upon such conditions would be enormous. The matters 

 worn off, being carried into the neighboring depths, and 

 there deposited, became the components of the earliest 

 stratified rocks, the first series of which is the Gneiss and 

 Mica Slate System, or series, examples of which are ex- 

 posed to view in the Highlands of Scotland and in the 



