338 
THE GEOLOGlSTo 
Pethervvin group," and is not supposed to have any equivalent in 
South Devon.* Accepting this chronology, at least for the present, 
there are, when considered geographically as well as chronologically, 
what may be termed five fossiliferous Devonian areas in the two 
counties, namely, one of the " Plymouth" age, in each of the districts, 
South Devon, Korth Devon, and Cornwall ; and one of the " Barn- 
staple" age, in each of the two last; these, as a matter of convenience, 
may be termed Lower South Devon, Lower North Devon, Lower 
Cornwall, Upper Korth Devon, and Upper Cornwall. 
Three hundred and forty-seven species of fossils, belonging to 
ninety-seven genera: forty. nine families and nine classes of animals, 
all invertebrate, are recorded as having been found in the five areas 
taken together. Of these, two hundred and ninety-six species are 
peculiar to one or other of the ai eas ; and the remaining fifty-one 
common to two or more of them. Not a single species is common 
to all the areas ; and only one, a coral, to four of them. The num- 
bers found in each, local and peculiar, are as below : — 
L.S.D. L.N.D. L.C. U.X.D. U.C. 
Peculiar 191 5 7 50 43 
Total 226 15 15 78 73 
No more than eight species have been found common to Lower 
South Devon and Lower Cornwall, closely connected as they are 
chronologically and geographically. This, however, can scarcely be 
considered remarkable, since the mineral characters of the deposits 
are very dissimilar ; the Cornish beds are all but exclusively slates, 
whilst South Devon is rich in limestone. It is not easy to account 
for the fact that the two contemporary — scarcely- dissimilar, and not 
widely-separated — deposits of Lower South and North Devon have 
also no more than eight species in common ; and that whilst as 
many as two hundred and twenty-six species are found in the former, 
no more than fifteen occur in the latter. 
The organic connection between the upper beds of Devon and 
Cornwall is gTeater than in the case of any other pair of areas, and 
is what might have been looked for, from the facts that they are in 
all respects closely allied. 
Sixty-seven of the Devon and Cornwall species are recorded as 
occurring in continental Europe, and seven in North America. Six 
of the seven are included in the European sixty-seven, and one of 
the six has been found also in Australia : hence the number common 
to Devon and Cornwall, taken as a whole, and districts beyond the 
British Isles, is greater than that common to the five areas of the two 
counties, in the ratio of sixty-eight to fifty-one, — that is of four to 
three. 
Of the three hundred and forty-seven species, eight are Silurian 
forms and fifty-eight Carboniferous ; none of the former number are 
included in the latter. The remainder, 281, are intermediate in 
character to those characteristic of the two periods just named, as 
* Quart. Jour. Geol. Soc, vol. viii., p. 3. 
