338 



THE GEOLOGIST, 



Petherwin 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, North 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 North 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 : — 



Peculiar 

 Total .. 



L.S.D. L.N.D. L.C, 

 191 5 7 



226 15 15 



TJ.N.D. U.C. 

 50 43 

 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 greater 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, aod 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. 



