Hutt—On the Geological Age of the North Atlantic Ocean. 313 
great mass of the sedimentary materials of the Lower Silurian period lay over the 
region of the present Western Atlantic; just as, in the case of the Lower Silurian 
beds of Europe, the originating lands must have lain in the region of the Eastern 
Atlantic; and there is no reason to suppose that these two land areas were not 
connected, as the great extent of the deposits derived from them imply the exist- 
ence of large rivers draining continental areas. Land also lay over the region of 
the Arctic regions during the earlier part of the Silurian epoch; but this was ulti- 
mately submerged in Upper Silurian times, as shown by the extensive deposits of 
strata of this period, from North Devon to Prince Albert Land.* 
(c) I pass over the evidence to be derived from the distribution of the Devonian 
strata of North America; but examples from it might be cited (as in the case of 
the ‘“ Hamilton group”) of the swelling out in vertical dimensions towards the 
eastward, and attenuation, accompanied by the substitution of calcareous strata 
for sedimentary, towards the centre of that continent; all tending to show that, 
in Devonian as in Silurian times, the land areas lay in the region of the Atlantic, 
and the sea areas in that of Central and Western America. 
Having thus endeavoured to point out the deductions to be derived from the 
position and extent of the Silurian beds on either side of the Atlantic, I pass on to 
consider what inferences may be drawn from the position of the Carboniferous 
strata in the same portions of the northern hemisphere. 
(3) Carboniferous Group.—The evidence to be derived from the third factor—ot 
which I am making use—in the elucidation of this question, viz., the Carboniferous 
group, is not less determinate than in the cases of those preceding. 
(a) British Isles.—It is some years since I first drew attention to the fact of the 
remarkable swelling out in vertical thickness which the sedimentary strata of the 
Carboniferous epoch undergo within the region of the British Isles, when traced 
both towards the north-west and south-west coasts; and also how the Carboniferous 
limestone passes from its solid calcareous condition into such clastic beds as sand- 
stone or shale, in similar directions. The details need scarcely be repeated here, 
and I content myself with the following summary, taken from the sources above 
referred tot (Plate VIII., figs. 1 and 2). 
A general summary of the N. W. increments may here be given :— 
N.W. Lancashire.  §.E. Lancashire. N, Staffordshire. Leicestershire and 
arwickshire. 
Coal-measures, 4 F : 8460 7680 6000 8000 
Millstone oa Series, . - 5500 2500 500 100-800 
Yoredale Series, . ; 5 4670 2000 2300 
Total in feet, . ‘ 18,630 12,130 8800 8100-3300 
* Both Upper and Lower Silurian beds occur in Grinnel Land. 
+ The reader is referred to the ‘‘ Quart. Journ. Geol. Soc.,” vol. xviii., p. 127, &c., for full details ; 
also to ‘‘ The Phys. Hist. Brit. Isles,” p. 87; or, ‘‘ The Coal Fields of Great Britain,” 4th edit., p. 516. 
TRANS. ROY, DUB. SOO., N.S. VOL. II. 2 
