130 
and Mr. G. Sowerby, of the testacea obtained in the superficial 
lacustrine or fluviatile deposits at Cromer and Mundesley in Norfolk, 
Stutton, Grays, Ilford, and other places near London, it appears, 
that the proportion of recent shells in those accumulations is still 
greater than in the Norwich crag, exceeding 90 per cent., and, con- 
sequently, that they must be placed among the newer Pliocene 
strata. 
In a paper communicated to the British Association at Bristol in 
1835, Mr. Charlesworth adopted a similar chronological arrange- 
ment of the formations above the London Clay in the eastern coun- 
ties, placing the coralline crag at the bottom of the series, the red 
crag next in ascending order, then the Norwich (mammaliferous) 
crag, and, highest, the lacustrine strata. In that paper Mr. Charles- 
worth states, that the proportion of recent to extinct species had 
not then been determined ; and Mr. Lyell remarks, it is satisfactory 
to find, that the paleontological test of age, derived from the relative 
approach to the recent Fauna, is perfectly in accordance with the 
independent evidence drawn from superposition and the included 
fragments of older beds. 
The memoir contains also a general comparison of the fossils of the 
crag with those of the faluns of Touraine. When M. Desnoyers, in 
1825, assigned a contemporaneous origin to both these formations, 
Mr. Lyell dissented from the conclusion, Ist. because the per-centage 
of recent species then ascribed to the crag, and determined chiefly 
from fossils of the Norwich beds, was greater than that of the Tou- 
raine deposit; and, 2ndly, because the fossils are not only almost 
entirely of distinct species, though only 300 miles distant from each 
other, but that the Fauna of the crag has a northern aspect, and 
that of Touraine an almost tropical character. A recent examina- 
tion, by Mr. 8. Wood, of a series of Touraine shells procured from 
M. Desjardin by Mr. Lyell, has proved, that there are not 10 per 
cent. of species identical with sheils of the crag; but an examination 
of the same series by Mr. G. Sowerby and the author has led to the 
conclusion, that the recent species are in the proportion of 26 per 
cent. Mr. Lyell, therefore, now accedes to the opinion of M. Des- 
noyers, that the red and coralline crag may correspond in age, ge- 
nerally, with the faluns of Touraine; and he is of opinion that the 
difference in the character of the two Faunas may be explained by 
there having existed at that epoch, a more equable climate, similar 
to the one experienced at present on the east coast of South 
America, where, in lat. 39°, occur, in a living state, a large Oliva, a 
Voluta, and a'Terebra; and that a geographical barrier, like that of 
the Isthmus of Suez, which separates the widely different Faunas of 
the Mediterranean and the Red Sea, may have intervened between 
the region of the crag and the faluns of 'Touraine. 
The paper concludes with a list of the testacea of the Norwich 
crag, determined by the author, Mr. S. Wood, and Mr. G. Sowerby*. 
* The memoir is printed in the Magazine of Natural History forJuly, 1839. 
