260 Paleo-Geological and Geographical Maps of the British Islands. 
must for a long lapse of time have been a continental area, whence was derived to a 
large extent the sediment of which many of our formations are composed ; and, 
secondly, that the Old Highland districts of the British Isles, once they had sprang 
into existence as such, ever after endeavoured to retain their ascendency.* This 
is the case with the mountains of North Wales, those of the Scottish Highlands, 
and of Donegal, Galway, and Wicklow, in Ireland, which all rose into mountain 
forms or elevated positions during that long interval of time which elapsed between 
the close of the Lower, and the commencement of the Upper Silurian epochs.+ 
Notwithstanding the enormous amount of waste to which these old mountain 
groups have been subjected, it is doubtful if at any time subsequently they were 
completely buried beneath more recent strata. In several instances, however, this 
was nearly being the case ; as, for example, during the epochs of deep depression in 
the Upper Carboniferous and Cretaceous periods. 
The first idea above referred to is one of great interest, and seems to run counter 
to the prevalent theory, that the existing oceans have been such from very remote 
geological periods. If this were the case, the existing Continents must equally 
have been Continents throughout an equal distance of time ; but, if so, how could 
they have been covered so largely by marine strata, belonging to Silurian, 
Devonian, Carboniferous, Jurassic, Cretaceous, and Eocene Tertiary times? 
The conclusion has been forced on my own mind, that the North Atlantic was 
mainly land during the Laurentian, Cambrian, and Lower Silurian periods, and 
was the source of the sediment of which these great formations are composed. It 
probably first assumed large proportions as a sea or ocean, when so much of the 
then sea became land, namely, at the close of the Lower Silurian period ; but there 
are grounds for believing that it was largely in the condition of a land surface in 
still later times, namely, during the Carboniferous, Permian, Triassic, and Jurassic 
periods, as evinced by the thickening of the sediment both towards the north-west 
and south-west of the British Islesg This great continent of Atlantis was the 
parent of much of the strata which now overspreads the plains of Britain 
and of the adjoiming continental areas. With the Cretaceous period its per- 
manently oceanic form and features set in, and were vastly extended during that 
and the succeeding period of the nummulitic limestone. 
* Prof. Sir A. Ramsay has shown that the mountains of North Wales became such before the Upper 
Silurian period, and it is doubtful if they were ever subsequently completely buried under strata of any 
newer formation.—See “ Phys. Geol. and Geog. of Gt. Britain,” 4th edit. 
t « Phys. Geol. and Geog. of Ireland,” p. 123 et seg. (1879.) 
{See Maps, Plates XXVIII. and XXXII. 
$I have shown this to have been the case with reference to the Carboniferous Rocks.—Quart. Journ., 
Geol. Soc., vol. xviii, p. 142, and of the Lower Secondary Rocks, /bid., vol. xvi., p. 63 et seg. 
