516 Geological Society : — Anniversary Address . 



occasional intercalation or juxta-position of stratified materials is 

 ascribed to the action of currents on materials 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 la- 

 teral pressure from drifting ice, especially where extremely con- 

 torted 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 cliffs. 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 

 deposits, which occur about the level of low water below the drift ; 

 but at Mundesley they are partly above it, and the freshwater shells 

 which they inclose being nearly all of British species, show that they, 

 as well as the contemporaneous drift, all belong to the newer Plio- 

 cene period. 



In an Address formerly delivered from this chair, in 1836, and 

 in a subsequent edition of his " Principles of Geology," as well as in 

 his " Elements," Mr. Lyell has called our attention to some differ- 

 ences of opinion which had been expressed by several eminent con- 

 chologists 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 results at which M. Deshayes, Dr. Beck, 

 and others seemed to have arrived, that their announcement was 

 calculated materially to impair our confidence in the applicability of 

 the chronological test so much relied on by Mr. Lyell for the clas- 

 sification of the tertiary formations ; namely, that derived from the 

 proportional number of recent and extinct species discoverable in 

 each deposit. In the hope of arriving at some definite conclusion 

 on this important point, Mr. Lyell visited Norfolk and Suffolk du- 

 ring the last year, and having obtained a considerable collection 

 from the crag near Norwich and Southwold, he instituted, with the 

 assistance of Mr. Searles Wood and Mr. George Sowerby, a thorough 

 comparison between them and recent species. The fossil shells of 

 this formation, which the author calls the Norwich crag, are partly 

 marine, and partly freshwater, and indicate a fluvio-marine origin, 

 and the proportion of living species was found to be between 50 and 

 60 per cent. This deposit, therefore, the author refers to the older 

 Pliocene period. A similar examination was then made of 230 species 

 of shells from the Red Crag in Mr. Wood's museum, and it was found 

 that 69 agreed with living species, being in the proportion of about 

 30 per cent. This group therefore Mr. Lyell ascribes to the Miocene 

 era. A collection of 34-5 species of Coralline Crag shells in Mr. 

 Wood's cabinet was then compared in like manner, and sixty-seven 

 were determined to be identical with recent species, being about 19 

 per cent. Mr. Lyell, therefore, considers that the Coralline Crag is also 



