20 
THE GEOLOGIST. 
Table I., to whicli attention has so frequently been directed, repre- 
sents, so far as is at present known, the absolute distribution of the 
fossils in the two counties in which they occur ; but, for purposes of 
geological chronology, it is probably of greater importance to ascer- 
tain their relative distribution, which may differ widely from that 
shown by the figures, since the various classes of animals represented 
in the fossil series were not equally rich in species, and perhaps 
difiered much in, what may be called, their distributivity. 
The relative distribution is exhibited in Table iV., which has been 
calculated from the data contained in Table I., thus : the total num- 
ber of species in each class is put = 1000, and the figures in the 
other columns equated to this. 
E-anged in descending order, according to their relative specific 
prevalence in each era, the classes stand thus :* — 
Lower South Devon : Zoophyta, Amorphozoa, Crustacea, Gastero- 
poda, Brachiopoda, Bryozoa, Cephalopoda, Echinodermata, and La- 
mellibranchiata. 
Lower North Devon : Bryozoa, Brachiopoda, Zoophyta, and La- 
mellibranchiata. 
Lower Cornwall : Amorphozoa, Crustacea, Zoophyta, Echinoder- 
mata, Brachiopoda, and Gasteropoda. 
Upper North Devon : Lamellibranchiata, Echinodermata, Bryozoa, 
Brachiopoda, Gasteropoda, Cephaloda, Crustacea, and Zoophyta. 
Upper Cornwall : Cephalopoda, Lamellibranchiata, Gasteropoda, 
Brachiopoda, Bryozoa, Crustacea, iEchinodermata, and Zoophyta. 
Both relatively and absolutely each class has its maximum specific 
development in South Devon, with the exception of Lamellibranchiata 
only, which has its greatest specific variety in Upper North Devon. t 
South Devon is the only area in which each of the nine classes oc- 
curs ; Lower Cornwall and Lower North Devon are each poor in 
classes as well as species, the latter yielding representatives of four 
classes only. 
When ranged in descending order, so as to show, relatively, the 
transmission of species from the Devonian to the Carboniferous era, 
the classes stand thus : — Bryozoa, Echinodermata, Brachiopoda, 
Gasteropoda, Cephalopoda, Crustacea, and Lamellibranchiata. And 
when similarly arranged for the species derived from the Silurian 
Fauna, they take the following order : — Zoophyta, Lamellibranchiata, 
Cephalopoda, and Brachiopoda. 
The class Amorphozoa is the only one in the Devonian Eauna 
which does not contain either Silurian or Carboniferous species. { 
From Table IV. it appears that fifty-six genera are peculiar to one or 
other of the three areas Lower South Devon, Upper North Devon, 
and Upper Cornwall ; and that, of these, forty-six, or very nearly one- 
half the total ninety-seven, are restricted to Lower South Devon. 
No genus is confined to Lower North Devon or Lower Cornwall. 
* See in Table IV. the columns headed " Totals." 
X See in Tables I. and IV. the columns headed " Totals." 
t See in Table IV. the columns headed " Silurian" and " Carboniferous." 
