Paleo-Geological and Geographical Maps of the British Islands. 269 
gray marls, with earthy calcareous bands (“cornstones ”), and red or purple sand- 
stones. Fish remains are present in the cornstones, but some examples of Lingula 
in the lower beds, and of Serpula in the upper, are all the evidences of inverte- 
brate life which, up to the present, they have presented to us. 
Tn South Devon the limestones are more massive, but it is not till we examine 
the sections in the Meuse and Ourthe, in Belgium, that we are able to appreciate 
the extent to which marine limestones were developed at this period. 
Relations with the adjoining Formations.—Confining our attention to the region 
of the south of England, the Devonian strata may be considered as forming a com- 
plete connecting series with the Upper Silurian and Devono-Silurian beds 
below and the Carboniferous beds above. Over this region, deposition of sediment 
appears to have proceeded with but few interruptions, of which none are marked 
by visible physical breaks. After the close of the Silurian period, depression went 
on, and various kinds of sediment were formed over the floor of the sea-bed, 
during slow subsidence over this area. Meanwhile the fauna of the previous 
period, modified as regards species, but largely similar as regards genera, 
re-appeared under new forms; and as Mr. Lonsdale long ago observed, presents 
generally a facies, intermediate between that of the Carboniferous, on the one hand, 
and of the Silurian, on the other. Mr. Etheridge recognises about 550 species as 
belonging to the British Devonian group. 
Absence of Devonian Beds i the North and West of the British Isles.—The 
- absence of representatives of the marine L)evonian beds of the south of England 
over the Irish and Scottish areas is a circumstance which, in my opinion, can only 
be satisfactorily accounted for in one way, namely, that these areas had been 
elevated into dry land during the time that the south of England and adjoining 
continental regions were submerged beneath the waters of the Devonian sea, and 
became the receptacles of Devonian sediment.* As confirming this view we have 
the fact that the Upper Devonian, or Old Red Sandstone proper, is everywhere 
unconformable to the beds on which it rests in Ireland and Scotland, whether 
these belong to the Devono-Silurian or still older formations.+ There is, therefore, 
in these countries a gap, or hiatus, of a very decided character, which is not the 
case in Devonshire, where the whole series, from the top of the Silurian to the base 
of the Carboniferous series, is complete. This northern and western hiatus is, in 
fact, filled up in Devonshire owing to the presence of the Lower and Middle 
Devonian beds, which are absent in Ireland and Scotland. 
* This view was first proposed in the Geological Magazine, and was afterwards more fully unfolded in 
the paper above cited, and in the Trans. Roy. Dublin Soc., vol. i., antea p. 147, &e. 
t This is distinctly enforced by Sir R. Griffith as regards Ireland, and is exemplified in many sections, 
especially those of the Dingle promontory ; and by Professor Geikie as regards Scotland. There may, 
also, be a slight unconformity at the base of the yellow sandstone in S. Wales, in keeping with that of 
the adjoining Irish area. 
