16 



THE GEOLOGIST. 



somewhat more than as two to one ; that is, thev 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 absolutely, and in a high ratio, exceed those 

 belonging 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 w^hich 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 

 W'ords, 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 siugle area. Lower 

 jN'orth 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 difi'erent combinations, 

 namely, ten tv>^o 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, is'ot a single species 

 of this ancient Eauna is common to the five areas, and only one, the 

 coral Uyatlwphyllum 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 L'pper 

 Cornwall have the greatest, and Lower South Devon and Lower 

 Cornwall the least, number in common ; in the former a total of 

 se venteen, 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, whiUt in Lower Cornwall the fossiliferous beds are all but 

 exclusively argillaciHMis — and there are very few organic remains in 

 connnon ; a marked instance, probably, of the influence of the mineral 

 character of the ancient sea-bottom on organic existence. Thouah 



