Page:A Treatise on Geology, volume 1.djvu/157

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CHAP. VI.
PALÆOZOIC STRATA.
141

Western Districts. Eastern Districts. Total Number of Species in each Class.
Car-
digan.
Mar-
loes.
Fresh-
water.
Haver-
fordwest.
Carmar-
then.
Llan-
deillo.
Builth. Usk. Tort-
worth.
May-
hill.
Wool-
hope.
Abber-
ley.
Mal-
vern.
Annelida 4 2 1 2 3 3 3 3 2 4 5 9 13
Crustacea 9 3 16 1 24 4 10 3 3 9 6 14 28
Cephalopoda 3 2 2 16 4 10 3 3 9 6 14 28
Heteropoda 5 2 4 4 3 2 3 4 6 10
Pteropoda 1 1 2 1 1 1 2 2 3
Gasteropoda 11 6 1 21 5 13 6 7 13 4 26 44
Lamellibranchiata 12 7 1 1 30 6 24 1 9 18 12 25 45
Brachiopoda 19 6 24 1 61 28 34 8 32 51 40 63 97
Echinodermata 2 8 2 2 1 1 2 1 4 15
Polypiaria 1 17 2 18 1 23 12 26 1 19 34 22 29 53
Number of distinct species in each districts. 5 81 29 73 4 187 72 128 30 76 143 107 195

If, taking the same 353 species, we inquire into their distribution through the strata of the eastern region (in which deposits are most sharply defined and present the greatest variety of mineral composition) we have the following table:—

Anne-
lida
Crus-
tacea
Cepha-
lopoda
Hete-
ropoda
Ptero-
poda
Gaste-
ropoda
Lamelli-
branchiata
Brachio-
poda
Echino-
dermata
Polyp-
iaria
Number of distinct species in each districts.
Dowston sandstone 1 1
Upper Ludlow 7 10 12 4 2 16 19 20 1 5 96
Aymestry rock 6 5 2 11 12 28 14 78
Lower Ludlow 1 6 3 2 4 9 27 16 68
Wenlock limestone 2 11 7 2 1 4 9 38 2 40 116
Wenlock shale 3 8 2 1 5 12 32 1 11 75
Woolhope limestone 1 2 1 1 20 4 29
Caradoc (Upper) 2 or 3 4 1 3 10 1 29 2 13 66
Caradoc (lower) 1 2 1 2 3 3 12
Trap
Black shale 4 4
Lowest sandstone

The maximum of variety appears in the Wenlock