JAMES REID ON MARINE ORIGIN OF OLD RED SANDSTONE. 25 
We might refer to the red sandstones and conglomerates of the 
Cambrian of Wales and the north-west of Scotland, as well as to 
those of the Devonian of New York (6000 feet in thickness), as 
deposits rivalling, if not exceeding, in extent similar deposits which 
characterise the Old Red Sandstone of Scotland. 
The injurious effects produced by peroxide of iron upon certain 
organic remains are referred to by Dr. Hunter as follows :—“ Per¬ 
oxide of iron is also unfavourable to the preservation of organic 
remains, and may in many cases account for their disappearance. 
Lately, when examining a few cut corals which had been imperfectly 
cleaned from this substance, . . I found that the smooth surfaces 
had in the course of a few hours been largely bitten into.” * 
The plant remains of Turin Hill (Forfar) occur in the form of 
pseudomorphs of iron, and if we suppose a dissolving agent of this iron 
to permeate the strata, we can understand the manner in which 
all traces of the original plants would disappear. Indeed, in localities 
where peroxide of iron is present, numerous shreds of fossil plants in 
the last stage of disappearance are not unfrequently met with. 
It may therefore be inferred that the presence of peroxide of iron 
in the waters of the Old Red Sandstone proved a bar to the entrance 
of the molluscan fauna of the period, and that adventurous mollusks, 
braving the unhealthy waters by penetrating therein, paid the penalty 
of their rashness by utter annihilation. 
That recent representatives of the ganoids of the Old Red Sand¬ 
stone inhabit rivers and lakes is by no means a proof of the fresh¬ 
water origin of the latter fishes. The immense interval of time 
implied by the comparison renders its value somewhat problematical. 
The salmon of our rivers, whose first appearance dates from the 
chalk of the cretaceous period, is a case in point. Besides, if we 
consider that Polypteriis^ Ceratodus^ and Lepidosiren are of world¬ 
wide distribution, it is difficult to believe that their present locatio?is 
—namely, the Nile and West Coast of Africa, Brazil, and Queens¬ 
land—could be reached by fresh-water means. The life-history of 
these obscure representatives of the “ age of fishes ” would probably 
show that they preserved their existence in the “ struggle for life ” by 
a successful adaptation to new conditions during the change from 
marine to fresh-water conditions, while their less-favoured contem¬ 
poraries succumbed. 
THE INTRODUCTION AND GEOGRAPHICAL DISTRIBUTION OF THE 
OLD RED SANDSTONE FISHES. 
With regard to the introduction and geological distribution of the 
fishes of the Old Red Sandstone, the case of the “ lake theory ” dis- 
* Trans.y Geol. Socy. of Glasgow. Vol. VIII., Part I. 1886. Page 163. 
