LECTURES ON GEOLOGY. 245 



ence of its fossils from those of the succeeding tertiary group, in 

 which shells are found identical v/ith those now inhabiting the 

 earth. Some of the tertiary strata are reared in a vertical position 

 in the Isle of Wight, and others are laid horizontally upon them. 

 The upper part of Headen Hill, at 400 feet above the sea, is a stra- 

 tum of fresh-water shells, 55 feet thick. The shells of the Suffolk 

 crag, the latest of the British tertiary strata, are so perfect that they 

 have hardly lost their colours, and yet most of them are now only 

 found in hot climates. The stones of which Stonehenge is formed 

 belong to the same formation as the crag. 



All these formations, except the primary, and a few of the 

 transition groups, bear most evident marks that they were formed 

 by the slow and gradual deposition of their materials upon the 

 bottom of lakes or seas j but over the whole of them we find 

 extended a bed of gravel, consisting of rounded fragments of the 

 whole series, even of the primary strata, and containing the remains 

 of recent as well as of extinct quadrupeds, not petrified, and but 

 little altered in consistence. From the almost universal extent of 

 this stratum over the world, and the internal proofs it bears of its- 

 recent origin, geologists are generally agreed in referring it to the 

 period of the Noachian Deluge, and have given it the name of 

 diluvium. Other gravel beds, of partial extent, and referrable to. 

 causes still in action, are termed alluvions. 



In this country, some of the most remarkable effects of diluviaV 

 action are exhibited by the deep vallies which have been excavated 

 near Bath, and by the immense deposits of gravel, and granitic 

 boulder-stones which are spread over the midland counties from 

 their parent rocks in Cumberland. In like manner our eastern 

 shores are covered with fragments of Norwegian rocks, which have 

 also formed the source from whence the blocks which strew the 

 plains of Lower Germany have been derived. Similar masses, of 

 enormous size, have been torn from the Savoy Alps, and borne by 

 the rush of retiring waters across the Lake of Geneva, have rested 

 on the secondary strata of the Jura, 2500 feet above the level of 

 the lake. The bones of the mammoth have been found at Santa, 

 Fb, 8000 feet above the sea ; and the remains of horses and deer 

 were collected by the Tartars at twice that elevation in the eternal 

 snows of the Himmalaya Mountains. It is impossible for us to do 

 more than conjecture the causes that have operated in producing 

 such a flood; but from the scores, or scratches, on the surface of 

 the rocks both in Scotland and in the rocky mountains of North 

 America, as well as from the direction of the gravel beds and 

 boulders, we must conclude that during some period of its preva- 

 lence over the earth, the current set strongly to the south-east. 



The proofs of a more elevated temperature than we at present 

 enjoy in these northern latitudes, are very evident through the 

 whole of the secondary and tertiary strata -, but in none are they 

 more striking than in the diluvial deposits, from the circumstance 

 that in ihis stratum we find more animal remains whose congeners 

 are now inhabitants of hot climates. The abundance of perfect; 



