84 
RED CRAG. 
other lied Crag section.'^ Mr. Wood thus analyses the list of 
molluscat: — 
Mollusca from the Walton Grag. 
British and not Mediterranean - - - 13 
British and Mediterranean - - - - 61 
Mediterranean and not British ■ - - - 14 
Neither British nor Mediterranean - - - 10 
Not known living - - - - - 50 
Total ----- 148 
Reducing these figures to per-centages, for convenience of 
comparison with the Coralline Crag, the numbers are : — 
-— 
Coralline 
Crag. 
Walton 
Red Crag. 
British and not Mediterranean 
6T 
8*8 
British and Mediterranean 
- 
39‘4 
41-2 
Mediterranean and not British 
- 
13-0 
9-5 
Neither British nor Mediterranean 
- 
6T 
6-8 
Not known living 
- 
36-3 
33-8 
This table shows at a glance the slow change that the fauna is 
undergoing. Extinct species are fewer, southern species are 
more rare, and those be¬ 
longing exclusively to 
British or northern seas 
are more plentiful. The 
real extent of the differ' 
ence is, however, not 
brought out by this test. 
If we take into account 
the number of individuals, 
the increase of northern 
forms is very marked in 
the Crag of Walton, and 
we find also that charac¬ 
teristic Upper Pliocene 
forms, such as the re¬ 
versed whelk, Tro'plion 
antiquus (Fig. 11), occur 
plentifully, though quite 
unknown, either in Eng¬ 
land or in Belgium, in 
the older deposit. Most 
of the common mollusca 
of the Walton Crag are 
Fig. 11. 
Trophon antiquus^ Linn., 
reversed variety. 
Half natural size. 
* Prof. Prestwich observes, however, that fragments of Coralline Crag lime¬ 
stone do occur at Walton. 
t Supplement to the Crag Mollusca, p. 219. 
