PENGELLY — ON THE DEVONIAN AGE OF THE WORLD. 
339 
was first announced by Mr. Lonsdale a quarter of a century ago. 
The evidence, therefore, of the fossils on the chronology of the rocks 
in which they were inhumed is, first, that they are of an age inter- 
mediate to the Silurian and Carboniferous, — that is, they are the 
equivalents of the Old Red Sandstone, second, that they are 
organically connected with both these periods ; and third, that the 
connection is closer with the last than with the first. It seems 
probable, therefore, that whilst there is an ample development of 
Middle and Upper Devonian beds in the two counties, the lower 
group is less fully represented, and that the lowest beds of the district 
do not constitute the basement of the system. 
Assuming that the South Devon beds are more ancient than those 
of Petherwin or Barnstaple — and probably no geologist entertains a 
doubt on this point — it follows that all the fossils common to the 
first, and either or both of the others, must be regarded as contribu- 
tions from it to them: now this number is both absolutely and relatively 
greater in Petherwin than in Barnstaple. Again, of the two, the 
fatter area has contributed the greatest number of species to the 
Carboniferous fauna. Hence, tried by either of the above as tests of 
relative age, Petherwin and Barnstaple are not strictly contemporary, 
but the former is more ancient than the latter ; which is in unison 
with the opinion of Sir R. Murchison and Mr. Salter, based on other 
and, perhaps, more reliable data.* Indeed, Barnstaple has a smaller 
number of forms in common with South Devon than with the Car- 
boniferous beds ; hence it may be considered as rather belonging to 
the latter than to the Devonian series ; or, possibly may have 
to be regarded as " Passage beds" l^etween them. 
The Devonian fossils of Devon and Cornwall belong to ninety- 
seven genera, as has been already stated. Of these, twenty-four are 
(in Britain) peculiar to the Devonian era ; fourteen common to the 
Silurian and Devonian ; forty-one to the Silurian, Devonian, and 
Carboniferous ; and eighteen to the two last only. Hence thirty- 
eight genera die out, and forty- two commence existence in the 
Devonian age of the world. Several of the genera of the two last 
divisions pass upwards into Neozoic, and even recent times. Twenty- 
seven genera are recorded in British Silurian and Carboniferous lists 
which do not appear to have been represented in the Devonian fauna; 
an indication, perhaps, of the " imperfection of the geological record." 
Few of the genera, not restricted to it, have their maximum specific 
development in the Devonian era, and the period is remarkable for 
the specific poverty of its genera; it falls below both the Silurian 
and Carboniferous period, and especially the latter, in both these 
respects. Generically, as well as specifically, the Devonian fossils of 
Devon and Cornwall have rather Carboniferous than Silurian 
af&nities. 
According to the catalogues Devon and Cornwall have yielded 
nine species of sponges, belonging to four genera ; there is reason to 
* Silm-ia, 3rd Edition, page 300. 
