FAUNA OF THE CRAG. 
201 
were wanting, as far as was then known, in the glacial de¬ 
posits. Some few of these species have subsequently been 
found in the glacial drift, but the general conclusion of 
Forbes remains unshaken. 
The transport of blocks by ice, when the Red Crag was 
being deposited, appears to me evident from the large size 
of some huge, irregular, quite unrounded chalk flints, retain¬ 
ing their white coating, and 2 feet long by 18 inches broad, 
in beds worked for phosphatic nodules at Foxhallj four miles 
south-east of Ipswich. These must have been tranquilly 
drifted to the spot by floating ice. Mr. Prestwich also men¬ 
tions the occurrence of a large block of porphyry in the base 
of the Coralline Crag at Sutton, which would imply that the 
ice-action had begun in our seas even in this older period. 
The cold seems to have gone on increasing from the time 
of the Coralline to that of the Norwich Crag, and became 
more and more severe, not perhaps without some oscillations 
of temperature, until it reached its maximum in what has 
been called the Glacial period, or at the close of the Newer 
Pliocene, and in the Post-pliocene periods. 
Relation of the Fauna of the Crag to that of the recent 
Seas. —By far the greater number of the recent marine spe¬ 
cies occurring in the several Crag formations are still inhab¬ 
itants of the British seas; but even these differ considerably 
in their relative abundance, some of the commonest of the 
Crag shells being now extremely scarce—as, for example, 
JBuccinum Dalei —while others, rarely met with in a fossil 
state, are now very common, as Murex erinaceus and Car- 
dium echinatum. Some of the species also, the identity 
of which with the living would not be disputed by any 
conchologist, are nevertheless distinguishable’ as varieties, 
whether by slight deviations in form or a difference in aver¬ 
age dimensions. Since Mr. Searles Wood first described the 
marine testacea of the Crags, the additions made to that fos¬ 
sil fauna have not been considerable, whereas we have made 
in the same period immense progress in our knowledge of 
the living testacea of the British and arctic seas, and of the 
Mediterranean. By this means the naturalist has been em 
abled to identify with existing species many forms previous¬ 
ly supposed to be extinct. 
In the forthcoming supplement to the invaluable mono¬ 
graph communicated by Mr. Wood to the Palseontographi- 
cal Society, in which he has completed his figures and de¬ 
scriptions of the British crag shells of every age, lists will 
be found of all the fossil shells, of which a summary is given 
in the annexed table, p. 202. 
