Geological Society. 



489 



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 

 GO 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 

 t'lat 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 345 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 1 9 

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

 Miocene, although belonging to a more remote part of that period 

 than the Red Crag. Having obtained from M. Dujardin a collection 

 of 240 shells from the Faluns of Touraine, he found with Mr. George 

 Sowerby's assistance that the recent shells were in the proportion of 

 twenty-six per cent., so that he has now come round to the opinion 

 long ago announced by M. Desnoyers, that upon the whole the Crag 

 of Suffolk corresponds in age with the Faluns of Touraine, both be- 

 ing Miocene, although the species in the two countries are almost 

 entirely distinct, those of England having a northern and those of 



