OLD CONTINENTS. 583 



Chalk, and it may be even comprehending the additional time occu- 

 pied in the formation of the Tertiary strata. But this latter part of 

 the subject I propose to work out before long. 



One other point remains. I have elsewhere attempted to prove, 

 and the opinion is gaining ground in England, that this long conti- 

 nental epoch embraces at least two glacial episodes, as witnessed first 

 by the bowlder-beds of the Old Red Sandstone of Scotland and the 

 north of England, and secondly by the occurrence of similar deposits 

 containing far-borne erratic blocks and ice-scratched stones, in a por- 

 tion of that part of the Permian strata that is usually considered to 

 represent the German Rothliegende. Should this be finally admitted, 

 it may, on astronomical grounds, some day help us in the positive 

 measurement of geological time. 



Finally, let me rapidly pass in review what I think we know of 

 later terrestrial, as opposed to marine epochs, in the British and neigh- 

 boring areas of Europe. A wide-spred partial submergence brought 

 the old continent to an end, and during the Liassic and Oolitic epoch 

 (Jurassic) the Highlands of Scotland and other mountain-regions in 

 the British Islands formed, with some other European Palaeozoic 

 rocks, groups of islands, round which, in warm seas, the Jurassic 

 strata were deposited. These relics of an older continent, by deposi- 

 tion of newer strata and subsequent gradual upheaval, began to grow 

 in extent, and at length formed the great continental area through 

 which the mighty rivers flowed that deposited the strata of the Pur- 

 beck and Wealden series of England and the continent of Europe. 



A larger submergence at length closed this broad local terrestrial 

 epoch, and in those areas now occupied by Northern Europe (and 

 much more besides), the sea, during the deposition of groat part of 

 the Chalk, attained a width and depth so great that probably only 

 the tops of our British Palaeozoic mountains stood above its level. 



By subsequent elevation of the land, the fluvio-marine Eocene 

 strata of Western Europe were formed, including in the term fluvio- 

 marine the whole English series, embracing the London Clay, which 

 as shown by its plant-remains was deposited at, or not far from, the 

 mouth of a great river, which in size, and in the manner of the occur- 

 rence of some of these plants, may be compared to the Ganges. "With 

 this latter continent there came in from some land, unknown as yet, a 

 great and new terrestrial mammalian fauna wonderfully different from 

 that which preceded it in Mesozoic times, and from that day to this 

 the greater part of Europe has been essentially a continent, and in a 

 large sense all its terrestrial faunas have been of modern type. 



One shadowy continent still remains unnamed, far older than the 

 oldest of those previously spoken of. What and where was the land 

 from which the thick and wide deposits that form the Silurian strata 

 of Europe were derived? For all sedimentary strata, however thick 

 and extended in area, represent the degradation of an equal amount 



