2 2 TRANSACTIONS—PERTHSHIRE SOCIETY OF NATURAL SCIENCE. 
A marked distinction is observable between the rival theories in 
question. The “lake” theory, on the one hand, implies a new 
departure—from marine to fresh-water conditions,—and its inade¬ 
quacy to account for the introduction and geographical distribution 
of the fauna of the formation is conspicuously apparent. The 
“ marine ” view, on the other hand, presents us with a more un¬ 
broken continuity—physical and palaeontological—between the for¬ 
mations preceding the Old Red Sandstone in geological time and 
the Carboniferous succeeding it. 
We apply the term “ marine ” in this connection to shallow salt¬ 
water conditions—in a word, to “ Devonian sea margins,”—for un¬ 
questionably the conglomerates and sandstones of the S3^stem indicate 
shore-lines, and shallow water not far from land. 
We propose in the following part of our paper, first, to consider 
the theories advanced in regard to the origin of the Old Red Sand¬ 
stone, and, second, to review the Palaeontological and other evidence 
bearing upon the “fresh-water” or “marine” origin. 
THE OLD RED SANDSTONE : ITS ORIGIN. 
The late Sir A. C. Ramsay and Sir A. Geikie refer to the origin of 
the Old Red Sandstone in the following terms :—“ Before the deposi¬ 
tion of the Old Red Sandstone, . . . there is reason to believe 
that a wide and deep valley already existed between the Grampian 
mountains and the Garrick, Lammermuir, and Moorfoot range, and 
in this hollow the Old Red Sandstone was deposited.” * 
“ In the west and north-west of Europe the Silurian sea-bed was 
upraised into land in such a way as to include large inland basins. 
. . In the inland basins of the north-west a peculiar type of 
deposits termed the Old Red Sandstone is believed to have accumu¬ 
lated, f . . . Similar exposures are to be seen here and there 
round the flanks of the Cumberland mountains, which were not 
improbably covered over with Old Red Sandstonei and carboni¬ 
ferous rocks as the Lammermuir chain of Scotland was.” § 
Messrs. Coates and Macnair assume the existence during Silurian 
times of the great faults occurring on each side of the midland valley 
of Scotland, which, from the “ lake theory ” point of view, is justifi¬ 
able. The striking description of the manner in which the conglo¬ 
merates of the system were laid down shows how thoroughly, step 
by step, these authors have thought out their subject. Both in its 
conception and execution the paper in question is one which merits 
the closest consideration at the hands of geologists. 
* Sir A. C. Ramsay, The Physical Geol. and Geog. of Gt. Britain. 2nd Ed., 
1854. Pages 48, 49. 
+ Sir A.'Geikie, Textbook of Geology. 1882. Page 694. 
J The Old Red Sandstone here referred to is Upper Old Red Sandstone. 
§ Outlines of Geol. Brit. Isles. 1876. Page 24. (A. Geikie.) 
