OLD RED SANDSTONE OF WESTERN EUROPE. 347 
system ; while between their base and the top of the Upper Silurian formations 
lay the vast masses of lacustrine sandstones and conglomerates of the Old Red 
series, marking the lapse of a prodigious interval of time. I do not propose in 
the present memoir to enter into this disputed question. I believe, however, 
that some progress may be made towards a solution of the difficulty by a more 
thorough examination into the distribution and history of the deposits which 
admittedly belong to the Old Red Sandstone. 
At the present time these deposits, as they occur in Europe, are divided 
into three groups, Lower, Middle, and Upper, in accordance with the classi- 
fication proposed by Murcuison. To the Lower series are assigned the red 
‘sandstones, shales, and conglomerates which graduate downward into the 
Upper Silurian system, and which are characterised by cephalaspid and 
pteraspid fishes, and by large eurypterid crustaceans. In the Middle group 
are placed the flagstones and nodular clays of the north of Scotland, con- 
taining numerous dipterme and acanthodean fishes. To the Upper division 
‘are relegated the red and yellow sandstones, lying conformably below the 
Carboniferous system, and, when fossiliferous, containing such characteristic 
fishes as Holoptychius, Bothriolepis, and Phaneropleuron. Never having been 
able to find any stratigraphical support for this classification, I can hardly 
resist the suspicion that, plausible though the argument from fossil evidence 
appears, the threefold subdivision was unconsciously suggested by the seem- 
ingly well established threefold arrangement of the true Devonian rocks, 
and by the natural desire to establish a closer analogy between these rocks 
and the Old Red Sandstone. Murcuison asserted that in the north of 
Scotland a clear ascending series could be traced through the three groups 
of the Old Red Sandstone, though it neither went down so far as the top 
of the Upper Silurian series, nor reached up as high as the base of the Car- 
boniferous.* My own work in the centre and south of Scotland had proved 
the Old Red Sandstone to consist of two great divisions,—a lower passing 
down conformably into the Upper Silurian shales, and an upper graduating 
upward into the Lower Carboniferous sandstones, with a complete discordance 
between the two series.t Mr Jukes and Mr Du Noyer had made out a similar 
arrangement in the south-west of Ireland ; but no fossils had been found in the 
lower subdivision there, so that its title to rank as part of the Old Red Sand- 
stone had at least no paleontological support.{ In the southern half of Scot- 
land, however, the evidence both from fossils and from stratigraphical succes- 
* “Quart. Journ. Geol. Soc.” vol. xv. p. 493 et seg.; and “Siluria,” 4th edit. p. 250. 
t “Quart. Journ. Geol. Soc.” vol. xvi. (1860), p. 312. 
{ See “Explanation to Sheets 160, 161,171, and 172 of the Geological Survey of Ireland” (1863). 
It is much to be wished that some fossil evidence could be obtained to fix the limit of the Upper Silurian 
series in the south-west of Ireland. The lithological argument seems to favour the classification adopted by 
Mr Juxes, for a great part of his Dingle beds would answer well for much of the Lower Old Red Sandstone. 
