2 8 TRANSACTIONS—PERTHSHIRE SOCIETY OF NATURAL SCIENCE. 
It therefore appears that, even in the red coloured rocks of the 
Old Red Sandstone of Britain, marine fossils are not absent, and in 
the Canadian formation marine shells occur in considerable numbers. 
We mention the interesting fact, that ‘‘a large lamellibranch, closely 
resembling the Ajiodonta of the Old Red Sandstone of Ireland, is 
met with in the Devonia7i of New York.” * 
THE KEY TO THE DEVONIAN QUESTION. 
In the interbedded limestones and sandstones of the Russian 
Devonian, containing marine shells and Old Red Sandstone fishes, 
we find the key to the true position of the Old Red Sandstone and 
Devonian. Not only so, but as the fish-bearing sandstones contain 
no marine shells, we can understand the fact of the absence of mol- 
luscan remains in the formation of Caithness. 
It is highly probable that the sandstones and shales of the Russian 
Devonian represent the spawning-grounds of the fishes of the for¬ 
mation, and in certain zones of the Caithness flagstones and shales 
similar conditions are probably met with. We know that in the 
spawning season numerous dead fishes are seen in our rivers, and 
the fact may to a great extent account for the greater number of 
fishes which occur in the sandstones of the Devonian than in its 
deep-sea deposits. 
The exigencies of the “lake” theory require a sudden covering 
up of the fishes of the Old Red Sandstone to ensure the high state 
of preservation in which they occur; but an inland fresh-water lake 
does not seem to afford an adequate medium for the purpose. It is 
impossible to conceive the manner in which dead fishes could, in 
fresh water, be preserved entire during the formation of sandstones 
and shales, of several feet in thickness, in a tideless inland lake. A 
marine formation, however, presents a striking contrast. The anti¬ 
septic properties of salt water would prevent decomposition for a time 
sufficient to allow the diurnal tides, laden with sand and mud, in 
their ebb and flow, to cover up immense numbers of the fishes in 
question, and would likewise tend to their preservation for some 
time afterwards. 
Referring to the Old Red Sandstone of the Moray Firth area, 
Hugh Miller states:—“A bed of pale yellow saliferous sandstone, 
settled, tier over tier, on a bed of stratified clay, and was itself overlaid 
by another bed of stratified clay in turn, and this upper bed had also 
its organisms. . . . Some of the sandstones of the system are 
strongly saliferous.” f To one who has seen the large stratum of 
* Sir A. Geikie, Textbook of Geology. 1882. Page 706. 
t The Old Red Sandstone. 4th Edit., 1850. Page 285. 
