Supercretaceous Formations. 65 



or many transient advances of water over dry land, and therefore pro- 

 poses., as Mr Murchison and others have already done, to substitute the 

 term of Drift for that of Diluvium, which many other writers have as- 

 signed to it. The drift, or diluvium, is of two kinds : one composed of 

 sand, loam, clay, and gravel, all regularly stratified ; the other consist- 

 ing of clay, not divided into beds, and containing boulders of granite, 

 trap, and other rocks. 



This clay is known on the east and north-east coast of Scotland by the 

 name of Till. He considers the stratified drift and till to be contempo- 

 raneous formations, and compares the latter to moraines formed at the 

 termination of glaciers. He imagines that drifted masses of ice, charged 

 with earthy matter and fragments of rock, may have deposited the till as 

 they melted in still water, and the occasional intercalation or juxtaposi- 

 tion of stratified materials is ascribed to the action of currents on mate- 

 rials also falling from melting icebergs. 



Mr Lyell refers the complicated bendings and tortuous foldings of many 

 beds of this formation near Mundesley and Cromer to lateral pressure 

 from drifting ice, especially where extremely contorted beds repose upon 

 undisturbed and horizontal strata. But he admits that some of them may 

 be due to landslips of ancient date, and which had no connection with 

 the present line of clifTs. At the bottom of the boulder-formation, and 

 immediately above the chalk, extensive remains of a buried forest occur, 

 the stools of the trees being imbedded in black vegetable earth. From 

 the position of this forest, a vertical subsidence of several hundred feet 

 and a subsequent rise of the land to the same amount is inferred. This 

 forest and a bed of lignite are connected with fluviatile or lacustrine de- 

 posits, which occur about the level of low water below the drift ; but at 

 Mundesley they are partly above it, and the fresh- water shells which they 

 inclose, being nearly all of British species, shew that they, as well as the 

 contemporaneous drift, all belong to the newer pliocene period. 



In an address formerly delivered from this chair, in 1836, and in a sub- 

 sequent edition of his " Principles of Geology," as well as in his " Ele- 

 ments," Mr Lyell has called our attention to some differences of opinion 

 which had been expressed by several eminent conchologists as to the 

 number of fossil shells of the Crag of Norfolk and Suffolk which could be 

 identified with living species. So great was the discordance of the re- 

 sults at which M. Deshayes, Dr Beck, and others seemed to have arrived, 

 that their announcement was calculated materially to impair our confi- 

 dence in the applicability of the chronological test so much relied on by 

 Mr Lyell, for the classification of the tertiary formations ; namely, that 

 derived from the proportional number of recent and extinct species disco- 

 verable in each deposit. In the hope of arriving at some definite conclu- 

 sion on this important point, Mr Lyell visited Norfolk and Suffolk during 

 the last year, and having obtained a considerable collection from the 

 Crag near Norwich and Southwold, lie instituted, with the assistance of 

 Mr Searles Wood and Mr George Sowcrby, a thorough comparison be- 



VOL. XXX. NO. MX. JANUARY 1841. E 



