Hutt—On the Geological Age of the North Atlantic Ocean. 307 
I select these three dominant groups for my purpose ; first, because of their 
wide distribution over the land surface of the globe; second, because of the great 
vertical dimensions to which they attain; and thirdly, because (with the partial 
exception of the uppermost member of the Carboniferous system) of their marine 
origin, and as indicative of the former presence of oceanic waters wherever they 
are found within the limits to which these observations extend. 
(6) General Considerations regarding the Extent of Archean and Palewozoie Land and 
Sea.—Before proceeding, however, to localize my observations to the region of the 
North Atlantic and its bordering land, let me draw attention to one general result 
of far wider application. 
In some investigations into the extent of the Archzean, Silurian, and Carboniferous 
formations over the land-surface of the globe, I have been strongly impressed with 
the belief that there has been a very general interchange of land and sea during 
these periods. The areas occupied by these formations—whether at the surface or 
as overlain by newer strata—form an exceedingly large proportion of the existing 
continents and islands; and if we include the inferential extent of the areas pre- 
vious to denudation, these existing tracts, whether visible or concealed, would be 
largely extended. It would be impossible for me to enter into details in proof of 
this statement here; but it may be stated generally that the Archean rocks, or 
their presumed representatives, are so widely extended that they may be supposed 
to form the floor of the larger portion of the continents of Europe, Asia, Africa, 
North and South America. Now, these rocks, although consisting of gneiss or 
granite, hornblendic and micaceous schists, quartzites, and crystalline limestones, 
were (it is generally admitted) originally marine sediments, deposited over the 
floor of the then ocean, and derived from the waste of continental lands, which 
could only have occupied the positions of existing oceans ; and which, judging by 
the great vertical dimensions of the Archzan strata, must have been of propor- 
tionately vast horizontal extent.* 
It has, however, been argued by Dr. Wallace, that owing to the greater depth 
of the oceans as compared with the elevations of the land, and of the vastly greater 
volume of the ocean-water below the sea-level than of the land above that level 
(the proportion being as 1 to 36), whatever changes may have taken place in the 
relations of land and sea in past times were in the form rather of additions to, or 
modifications of, the pre-existing land, than by the upheaval of entirely new conti- 
nents in mid-ocean ;+ and such would, I admit, be the conclusion to be derived 
from a contemplation of the present distribution of land and sea. 
* Tt is right to state that Sir J. W. Dawson, F. R.§. (as I understand), regards the Archean rocks 
as formed of materials extruded out of the original crust in a molten condition, and afterwards meta- 
morphosed. It is difficult, however, to understand how such strata as schist, quartzite, and occasionally 
bands of limestone, could have originated in this way. 
+ .““ Geographical Distribution of Animals,” vol. i. p. 36. 
25 2 
