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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 
VOL. III. at 
