THE WORLD WITHOUT A BACKBONE. 231 



stretch of the herbless land, and no wing of bird or insect 

 agitated the fervid air. It was in the progress of this reign 

 of physical forces that I expressed the opinion that vegetal 

 life may have made its advent in the sea. 



The seons of the earth's infancy rolled on ; the first low 

 presages of coming continents had been ground to sediment ; 

 the only upraised examples of the primitive chemical precipi- 

 tates had been broken up and returned to the sea. Over the 

 ocean's floor was accumulating a mud which, in a later age, 

 should be baked to granite and gneiss those granites and 

 gneisses which in our times, have become forms so familiar. 

 We have before us the evidence that at least fifty to a hun- 

 dred thousand feet of such sediments accumulated. The sea- 

 bottom bent down under its load. The downward protuber- 

 ance reached into an intenser heat than could be endured. 

 Besides that, the very thickening of the crust permitted the 

 interior heat to make encroachments upward, as already ex- 

 plained. The water which saturated the strata of simple frag- 

 mental sediments became intensely heated under a high press- 

 ure. Alkaline substances were dissolved by the heated water, 

 and the hot alkaline solution acted powerfully on the rock- 

 materials. They were partly dissolved even silica was dis- 

 solved ; they were partly softened ; they were brought to such 

 a state that the atoms were free to arrange themselves accord- 

 ing to their affinities in their new situation. The old sub- 

 stances were therefore made over into minerals which did not 

 exist in the sediments before. These minerals were formed in 

 juxtaposition to each other; and when, in a later age, the 

 temperature subsided, the mineral mixtures which constitute 

 Eozoic rocks of the various kinds were at hand. They formed 

 granites, syenites, diorites, and similar rocks, in which the 

 metamorphosis was so complete that the lines of original bed- 

 ding were obliterated. They formed gneisses and schists in 

 which the metamorphism was less complete. Of course, if 

 there were any calcareous remains of tenants of the sea, these 

 were completely dissolved, and we have no means of proving 

 that they ever existed. 



