314 Hut1t— On the Geological Age of the North Atlantic Ocean. 
The rapid attenuation of the strata towards the centre of England is im some 
degree due to the proximity of a ridge of older rocks which occupied that part of 
the sea-bed throughout nearly the whole Carboniferous period ;* but the evidence 
as to the westerly position of the originating lands, as regards that of the British 
Isles, is too obvious to require that I should further insist on it. Sir C. Lyell has, 
in a masterly manner, pointed out the conclusions to be deduced from the pheno- 
mena which the Carboniferous series present to us, and it is unnecessary for me to 
do more than recall this fact. I therefore pass on to consider the evidence to be 
derived from the distribution of the Carboniferous beds of America. 
(b) North America.—Not less significant, as pointing towards a similar conclu- 
sion, is the distribution and changes in the characters of the Carboniferous strata 
of North America. The geologists of that country have supplied us with ample 
details for determining the directions in which the strata increase and decrease in 
thickness, and those in which calcareous and sedimentary strata predominate, or 
pass into one another. 
In treating of these details I shall adopt Professor Dana’s two divisions of 
‘“‘ Sub-carboniferous ” (corresponding to our Lower Carboniferous), and ‘‘ Carbon- 
iferous’’ (embracing our Middle and Upper Carboniferous divisions). Taking the 
beds in the ascending series, we commence with those of the Sub-carboniferous 
series. 
(c) Sub-carboniferous Sedimentary Beds—The greatest development of these beds 
south of the River St. Lawrence is in Pennsylvania, where the sandstones and 
shales reach a combined thickness of 5000 feet. These beds thin northwards, 
westwards, and south-westwards; or pass into beds of limestone, as shown by 
Professor Rogers. Thus, in Michigan, the sandstones and shales have dwindled 
down to 480 feet, in Virginia to a few hundred, while over the region of Arkanzas, 
Missouri, and Alabama, they are represented almost entirely by beds of marine 
limestone. 
But, perhaps, the greatest development of the sedimentary materials over the 
North American continent occurs in New Brunswick, where the land projects 
more prominently than elsewhere into the Atlantic waters. The well-known 
section of South Joggins, on the coast of the Bay of Fundy, shows a vertical series 
of strata of 4515 feet, while the whole series is estimated at a thickness of 14,570 
feet; of which, perhaps, one-half the amount may be considered as Lower Car- 
boniferous. This enormous swelling out in a N. E. direction, and the truncation 
of so great a mass of strata near the Atlantic shores, points unmistakably to the 
position of the orginating continental lands. While the attenuation of the Lower 
Carboniferous sedimentary strata towards the central continental area, and its 
* The position of this ridge is shown in Plates VI. and VII. of ‘The Phys. Hist. Brit. Isles.” For 
fuller details the reader is referred to my Paper in the ‘‘ Quart. Journ. Geol. Soc.,” vol. xviii. p. 127. 
