24 TRANSACTIONS—PERTHSHIRE SOCIETY OF NATURAL SCIENCE. 
ness, Morven, its chief summit (2313 feet above the sea level), is 
capped with Old Red Sandstone conglomerate. 
The upper Silurian of the counties of Edinburgh and Lanark— 
whose deposits range from 350c to 4000 feet in thickness—overlies 
the lower member of the system, and graduates upwards conformably 
into the Old Red Sandstone (Geikie). On the highland side of the 
valley the upper Silurian is not seen, but we have reason to believe 
that a depth of strata 4000 feet in extent could not—in a marine 
formation—occur as a local deposit. It must have extended along 
the central valley, graduating upwards conformably into the overlying 
Old Red Sandstone. The latter—probably by an overlap—is to be 
seen abutting upon the lower series of the Grampians. 
From the foregoing it will appear that in the Old Red Sandstone 
we have no new departure. The conformable deposition of Old Red 
Sandstone upon the preceding upper Silurian deposits implies a con¬ 
tinuation of, not a change from, similar conditions of deposition. 
PALEONTOLOGICAL AND OTHER CONSIDERATIONS. 
The fresh-water origin of the Old Red Sandstone is ascribed to 
“The character of the strata, the absence of unequivocally marine 
fossils, the presence of land plants, and of numerous ganoid fishes 
which have their modern representatives in rivers and lakes.” ^ 
We have, however, to point out that land plants, ganoid fishes, 
and marine shells occur indifferently in the Old Red Sandstone 
and Devonian. 
The assumption, so frequently met with, that strata of a red 
colour must necessarily be of fresh-water origin does not appear to 
be well-founded. 
In the Devonian of Russia red sandstones and marls containing 
numerous Old Red Sandstone fishes occur; while Professor Gosselet 
“ cites the case of the Devonian of the basin of the Dinant, where 
some beds are in one part red and barren of organic remains, and in 
another part of the same area are of the usual colour and 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.” f 
Sir W. Dawson refers to marine deposits of a red colour in the 
process of formation on the coast of Nova Scotia which at low tide 
extend for miles seaward. The red deposits, it is stated, derive their 
colour from peroxide of iron. “ We have here a perfect instance in 
a modern deposit of phenomena which we will have to notice in the 
most ancient rocks.” J 
* Sir A. Geikie, Textbook of Geol. 1882. Page 706. ^ Ibid. Page 71 
X Acadian Geology. 1855. Pages 28, 31. 
