THE OLD RED SANDSTONE. 9] 
of England, so carefully described by Mr. Murchison in his 
Silurian System, shells are very abundant ; and the fact may 
now be regarded as established, that the Tilestones of Eng- 
land belong to a deposit contemporaneous with the ichthyolite 
beds of Caithness and Cromarty. They occupy the same 
place low in the base of the Old Red; and there is at least 
one ichthyolite common to both,* and which does not occur 
in the superior strata of the system in either country — the 
Dipterus macrolepidotus.- The evidence that the fish and 
shells lived in the same period, and represent, therefore, the 
same formation, may be summed up in a single sentence. 
We learn from the Geology of Caithness that this species of 
Dipterus was unquestionably contemporary with all the other 
ichthyolites described ; — we learn from the Geology of Here- 
fordshire that the shells were as unquestionably contemporary 
with it.t These —the shells — are of a singularly mixed 
character, regarded as a group, uniting, says Mr. Murchison, 
forms at one time deemed characteristic of the more modern 
formations, — of the latter secondary, and even tertiary periods, 
—with forms the most ancient, and which characterize the 
molluscous remains of the transition rocks. Turbinated shells 
and bivalves of well nigh the recent type may be found 
lying side by side with chambered Orthoceratites and Tere- 
bratula. t 
The vegetable remains of the formation are numerous, 
but obscure, consisting mostly of carhonaceous markings, 
* Silurian System, part ii. p. 599. 
t In Russia, too, as shown by the recent discoveries of Murchison, 
the Old Red fishes of Caithness, and the Old Red shells of Devyon- 
shire, may be found lying embedded in the same strata, 
{ Silurian System, part i. p. 183. 
