MACKIE — ON THE BOTTOM-ROCKS. 



157 



the rise of the range of internal heat beneath sedimentary masses. 

 Were the old gneissic and granitoid rocks, that form the real nucleus 

 of our present lands, generated, expanded, and uplifted on these prin- 

 ciples and by those means 1 The evidence seems, to incline towards 

 this belief ; and if so, there must have been a world of land and sea 

 older than those remote ancestral island-domes and ridges that form 

 the earliest recognized traces of our present lands. For there must 

 have been lands to have furnished the materials of those sediments, 

 the heaping-up and over-piling of which gave increased range to the 

 subterranean heat ; and there must have been waves and ocean-cur- 

 rents to have abraded and worn them down, and to have transported 

 their finely divided particles into the abyss. And this still older 

 world-crust — whether life-less or life-full — has been melted up by 

 fervent heat, and fused into the adamantine foundations of the " ever- 

 lasting hills." 



Tt is not, however, on the ancient physical geology of our globe 

 that we wish to dwell at length in these chapters ; our object is to 

 treat more at large of the successive forms of the organized creatures 

 which have inhabited it, and to portray in our descriptions and illus- 

 trations the whole of the common forms of those abundant tribes 

 whose offices have been the most important in the past conditions of 

 our planet, and whose remains are characteristic of our principal rock- 

 masses. 



Still, we could not avoid considering, first, the formation and uprise 

 of those ancient lands of which these perished beings were the in- 

 habitants. Our thoughts must naturally first turn to the soil, the 

 shape and extent of the land, the form and elevation of the hills, the 

 flow of the rivers, if any existed, to the rivulets and rills, to the beat 

 of the waves on the shore, to the sunshine, the rain, and the dew ; 

 and then we seek to reclothe those ancient lands with plants, herbs, 

 and trees, to bedeck them with flowers, and to repeople them with 

 living creatures. Before we describe the first fossils we must think 

 of the first land and the first water that trickled over its surface. 

 We must think of the sky and the air, the sunshine and shadows, the 

 storms and calms of that first age of teriTstrial conditions. 



Philosophers tell us of a central heat, still sufficient within the 

 range of 800 miles below to fuse the most intractable rock. They 



