DESCRIPTIVE REMARKS. li 
Fosstts OF THE OLD Rep Sanpstone AND Devonran Rocks. 
Tue gradual transition from the uppermost grey Silurian strata into 
that of the red deposits, or Old Red Sandstone, has been clearly de- 
scribed by Sir R. Murchison and other Geologists as occurring near 
Ludlow where the thin beds or ‘‘ Tilestones,”’ partly of a reddish 
colour, with Ludlow fossils, clearly indicate the passage from one series 
of strata to the other. 
Additional examples of this succession have been also observed 
along the eastern edge of the Upper Silurian rocks in Hereford, Radnor, 
and Brecon, on the west flank of the Malvern and May Hills, and 
around the valley of Woolhope. 
In Shropshire this series of red sandstones with concretionary bands 
of impure arenaceous limestone, called ‘‘cornstone,’’? green and red 
clays and marls, and red conglomerates, resting conformably upon the 
Upper Ludlow rocks, are estimated at a thickness of 3,700 feet, being 
covered by the Carboniferous rocks of the Clee Hills; whilst in the 
counties of Monmouth and Brecknock it attains the great thickness of 
at least 10,000 feet, forming mountains nearly 3,000 feet high. The 
uppermost beds of this series of strata being conformably overlaid by 
the Carboniferous Limestone of the South Welsh coal basin. 
In the north of England the Old Red Sandstone so extensively de- 
veloped in the counties alluded to, rests unconformably on the Silurian 
rocks principally as a single band of coarse conglomerate lying between 
the Silurian and Carboniferous formations of the lake district of Cum- 
berland. 
The Old Red Sandstone of Scotland covers an extensive area. It bas 
been described as exhibiting two different types, north and south of 
the Grampian range. That of the south is abundantly developed be- 
tween the Grampians and the Cheviot Hills, and according to Professor 
A. Geikie is divisible into three groups. 
The Upper division, consisting of red and yellow sandstones, and 
conglomerates in Berwickshire and Haddingtonshire, resting unconfor- 
mably upon the Lower Silurian strata, passes gradually up into the base 
of the Carboniferous series; the strata of Dura Den, in Fifeshire, with 
its numerous fish remains, is also assigned to this group.* 
The Middle division consisting of red, green, and grey sandstones, 
flagtones, and conglomerates, includes the bituminous flagstones of 
Caithness and the Orkneys, strata in Elgin and Banff, and in the south- 
west of Ayrshire, where it is associated with contemporaneous volcanic 
rocks ; Pterichthys maor has been found in the upper part of the series. 
The Lower division, consisting of red, reddish-brown, and grey sand- 
stones and shales, with large masses of intercalated contemporaneous 
volcanic rocks, is exhibited in the Sidlaw and Ochil Hills, Pentland 
* The genera of fossil fish Holoptychius, Pamphractus, Glyptopomus, &c., with 
Paleopteris (Cyclopteris) Hibernicus, occurs in this group. 
