10 
THE GEOLOGIST. 
somewhat more than as two to one ; that is, tliey were then fifty 
times more abundant than at present in comparison with the other 
great class of Acephala. In like manner it is seen that, relatively to 
the Gasteropoda, the Cephalopoda were, in this early age of our 
planet, seventeen times more numerous than now. It may be added 
that, within the district under notice, the registered species of 
Devonian Brachiopoda ahsolutely, and in a high ratio, exceed those 
bc'longing to the same classes within existing British seas ; and the 
fact is the same for the world at large. 
The five columns of Table I., headed " Peculiar to," and distin- 
guished by the initials of the five areas respectively, show the number 
of fossil species which, so far as England is concerned, are peculiar 
to each ; from which it appears that the fossils of Devon and Corn- 
wall have a very limited and unequal distribution. Two hundred 
and ninety-seven species, that is, eighty-five per cent, of the whole, 
are peculiar to one or other of the areas, whilst no more than fifty 
species, or scarcely fifteen per cent, of the entire series, are distri- 
buted amongst them. Lower South Devon monopolizes no fewer 
than one hundred and ninety-one species in this way, or, in other 
words, fully sixty-four per cent, of the two hundred and ninety-seven, 
species thus limited, or fifty-five per cent, of all the known Devo- 
nians of the two counties are restricted to this single area. Lower 
North Devon, on the other hand, appears to be equally remarkable 
for its fossil poverty. 
It is unnecessary to say that five areas taken two, tliree, four, and 
five together are capable of making twenty-six different combinations, 
namely, ten two together, ten three together, five four together, and 
one five together. The ten combinations, however, headed " Common 
to," in Table L, are all that are required to show the distribution of 
the fifty species not confined to one single area. Not a single species 
of this ancient Fauna is common to the five areas, and only one, the 
coral CyatJiophyllum celticum, is found in each of four of them. The 
well-known coral Favosites cervicornis is the only fossil found in each 
of the three contemporary deposits of Lower South and North Devon 
and Cornwall. Of two areas only. Upper North Devon and Upper 
Cornwall have the greatest, and Lower South Devon and Lower 
Cornwall the least, number in common ; in the former a total of 
seventeen, and in the latter of eight species only. Dissimilar as are 
the organic distributions in these two pairs of areas, they are pro- 
bably just wliat might have been expected. In each pair the two 
areas are pretty closely connected geographically, and are supposed 
to be contemporary, as their names imply ; but in the former the 
mineral character is much the same in each area, and we have a 
greater organic similarity than ordinary ; in the latter the deposits 
are very unlike — Lower South Devon being rich in limestone as well 
as slate, whilst in Lower Cornwall the fossiliferous beds are all but 
exclusively argillaceous — and there are very few organic remains in 
common ; a marked instance, probably, of the influence of the mineral 
character of the ancient sea-bottom on organic existence. Thoufrh 
