The relation which these species (155, including the varieties) show to the Eed and Coralline Crags of Suffolk is as follows : —
Bi- Uni- valves, valves.
Common to the Red Crag 69 68 = 137 or 88 per cent.
Common to the Coralline Crag 54 33 = 87 or 56 "
We have before (ante, p. 352) seen that the number of species of the Red Crag found in the Coralline Crag was 62 per cent.
With regard to the proportion, in the Norfolk-Crag period, of existing species to those not known as living, the following is the result, after excluding the 16 varieties and doubtful species : —
Total. Living. Extinct. Proportion of extinct species.
139 130 9 6.5 per cent.
Comparing the three Crags, the respective proportions of extinct and living species of Mollusca in each is as under : —
Extinct. Living.
In the Norfolk Crag 6.5 93.5 per cent.
In the Red Crag of Suffolk 7.7 92.3 "
In the Coralline Crag 16.0 84.0 "
showing so close a relation between the Norwich and Red Crags as to afford good reason for considering them to be both of the same age*.
With respect to the geographical range of the 216 living species (exclusive of varieties and extraneous species) of the Red Crag, and of the 130 species of the Norwich Crag, some marked differences are noticeable, as shown in the following Table.
Table of Geographical Distribution of the Mollusca of the Bed and Norwich Crags.
Red Crag. Norwich Crag. Bi-valves.
Uni-valves.
Total.
Bi- Uni- valves, valves.
Total.
21 .. 19 = 40 18 ... 18 = 36
... 7 .. 10 = 17 7 ... 7 = 14
63 ... 72 = 135 42 ... 44 = 86
77 .. 80 = 157 42 ... 45 = 87
80 .. 76 = 156 37 ... 36 = 73
... 79 .. 88 = 167 33 ... 34 = 67
35 .. 49 = 84 18 ... 20 = 38
Special localities. — Africa, 1 South Africa, 1 ; West Indies, 1 Gulf of Mexico, 1 ; Japan, 3.
- Taking Aldeby to represent the upper division (or the Chillesford Sands)
and the lower beds at Bramerton the lower division (or the equivalent of the Red Crag of Sutton, Waldringfield, &c.) of the Norwich Crag, we have the following results : —
Total species.
Proportion of extinct to living species, per cent.
Aldeby 71 5.6 53 38
Bramerton 64 6 58 24
Numbers common to the Red Crag. Coralline Crag.
