Parr II. Sxcr. iii. (1) §2.] OLD RED SANDSTONE. 711 
Eurypierus and Pierygotus. The species of the former are small, but 
_ one of the latter, P. anglicus (Fig. 329), is found in Scotland, which 
must have had a length of five or six feet. 
§ 2—Local Development. 
Murchison, who strongly advocated the opinion that the Old Red 
Sandstone and Devonian rocks represent different geographical condi- 
tions of the same period, and who had with satisfaction seen the adoption 
of the Devonian classification by Continental geologists, endeavoured to 
trace in the Old Red Sandstone of Britain a threefold division, like that 
which had been accepted for the Devonian system. He accordingly 
arranged the formations as in the subjoined table: 
y 
(8 Yellow and red sandstones and conglomerates (Péterichthys major, 
Holoptychius nobilissimus, &c.)= Dura Den beds. 


oO 
| 
$8 
oe 
Mo Al. : 3 
a2 3 £|Grey and blue calcareous and bituminous flagstones, limestones, 
Mai { and red sandstones, and conglomerates (Dipterus, Osteolepis, 
Sag || Asterolepis, Acanthodes, Plerichthys, &c.)=Caithness flags. 
os 
" 2m # (Red and purple sandstones, grey sandy flagstones, and coarse 
S =) conglomerates (Cephalaspis, Pteraspis, Pterygotus)= Arbroath 
(3 ( flags. 
It is important to observe that in no district can these three sub- 
divisions be found together, and that the so-called “‘ middle” formation 
occurs only in one region—the north of Scotland. The classification, 
therefore, does not rest upon any actually ascertained stratigraphical 
Sequence, but on an inference from the organic remains. The value of 
this inference will be estimated a little further on. .AIl that can be 
affirmed from stratigraphical evidence in any Old Red Sandstone district 
in Britain is that a great physical and paleontological break can gene- 
rally be traced in the Old Red Sandstone, dividing it into two completely 
distinct series. 
As a whole, the Old Red Sandstone, where its strata are really red, is, 
_ like other masses of red deposits, singularly barren of organic remains. 
The physical conditions under which the precipitation of iron oxide took 
place were evidently unfavourable for the development of animal life in 
the same waters. Sir A. C. Ramsay has connected the occurrence of 
such red formations with the existence of salt lakes, from the bitter 
waters of which not only iron oxide but often rock-salt, magnesian lime- 
stone, and gypsum were thrown down.' He points also to the presence 
of land plants, footprints of amphibia, and other indications of terrestrial 
surfaces, while truly marine organisms are either found in a stunted con- 
dition or are absent altogether. Where the strata of the Old Red Sand- 
stone, losing their red colour and ferruginous character, assume grey or 
yellow tints and pass into a calcareous or argillaceous condition, they 
1 Professor Gosselet contends that the precipitation of iron might quite well have 
taken place in the sea, and he cites the case of the Devonian basin of Dinant, where the 
same beds are in one part red and barren of organic remains, and in another part of the 
game area are of the usual colours, and are full of marine fossils. But the red colour of 
the Old Red Sandstone is general, and is accompanied with other proofs of isolation 
in the basins of deposit. 
¥ 
