lxiv DESCRIPTIVE REMARKS. 
Middle Devonian group of the Rhine, and the same division in 
Belgium and France. 
The Devonian Crustacea are, in their general aspect, allied to those 
of the Silurian, the genera being nearly all similar. 
Whilst there are over 100 species of fossil fish in the Old Red 
Sandstone proper, in the Marine Devonian, three only are known, viz. : 
1. Phyllolepis concentricus, from the Meadsfoot group, Lower Devonian 
Slates of Cornwall.* 2. Holoptychius, from the same group, and 
Baggy, Upper Devonian. And 3. Onchus (?), fish bones and defence 
spines in Middle Devonian strata, east side of Ilfracombe Harbour.t 
FossIts oF THE CARBONIFEROUS Rocks. 
The series of strata included in the Carboniferous formation are in 
Britain usually grouped into four divisions; the lowest being the 
Lower Limestone shale, or Carboniferous slate, which is occasionally 
interstratified with ferruginous sandstones about 200 feet in thickness, 
these strata graduate downwards into the Upper Old Red Sandstone ; 
over this is the Carboniferous or Mountain Limestone, an aggregation 
of compact thick and thin bedded limestones, of various shades of red 
and grey, occasionally interspersed with shales, its thickness ranging 
from 500 to 1,500 feet. These two divisions form the lower portion of 
the series. Over them is the Millstone Grit, locally called Farewell 
yock, which usually consists of hard quartzose sandstones having a 
maximum thickness of 1,000 feet. Superimposed upon this is the Coal 
Measures, consisting of an Upper and Lower series, between which in 
the Somersetshire and South Welsh districts are the Pennant Sand- 
stones. 
The total thickness of the whole Coal Measure group in the first 
named district is estimated at 5,000 feet, and in some parts of South 
Wales at as much as 12,000 feet. 
The Carboniferous rocks are clearly exhibited in the great South 
Welsh Coal basin of Caemarthen, Glamorgan, and Monmouth ; and on 
a smaller scale in that of the Forest of Dean, and with certain mineral 
changes and an expansion of the lower shale in the county of Pem- 
broke. 
Towards the north, as observed in Shropshire and Flintshire, the 
lower portion of the series is more developed, a change which becomes 
still more evident in the range of strata from Derbyshire into York- 
shire and Northumberland, and especially so in the great central Car- 
boniferous depression of Scotland. 
* Pengelly, Report Royal Geological Society, Cornwall, 1860-65. 
+ Etheridge, Journal Geological Society, Vol. xxiii., pp. 606, 617, 677. 
