Hutu 
On the Geological Age of the North Atlantic Ocean. 309 
similar phenomena awaiting us. The Laurentian rocks stretch from Nova Scotia* 
and the coast of Labrador to the shores of the Great Lakes, and thence in a north- 
westerly direction to Kent peninsula, north of the Arctic Circle.t On either side 
they throw off strata of Lower Silurian or Lower Cambrian (Huronian) age, so 
that their presence at the surface amongst the Laurentian mountains is partly, at 
least, due to denudation; but Professor Dana is of opinion that some of the central 
portions of the Laurentian area never have been covered by newer strata, as the 
Potsdam sandstone of New York, lying at the base of the Silurian series, affords 
evidence of marginal conditions of deposition. 
These crystalline strata crop up in two places in Central America, in the Black 
Hills of Dakota, the Laramie range of Nebraska, and in the Middle Cordilleras, 
as shown by Mr. Clarence King.§ They also form a tract of country between 
the Alleghanies and the marginal oceanic region of the Atlantic. Thus it may be 
said that the whole of the fossiliferous strata of North America are set in a frame- 
work of Archzan bedded crystalline rocks; and we may consequently infer that 
these rocks underlie the newer formations, and stretch below the waters both of the 
Atlantic and Pacific Oceans for undefined distances (Plate VII., Fig. 1). 
(2) The Aretic Regions and Greenland.—Gneissose rocks, presumably of Laurentian 
or Archzan age, occur at C. Isabella and C. Sabine, at the entrance to Smith 
Sound; and, on the opposite coast of Greenland at Foulke Head, where they form 
the cliffs at the edge of the great Humboldt glacier.|| These beds pass below 
conglomerates and limestones of Upper Silurian age, which occupy large districts 
north of the Arctic Circle. Of the rocks which enter into the structure of the 
interior of Greenland we know but little, except that they are crystalline and 
hornblendic ; but whether of Laurentian or pre-Laurentian age is probably for 
ever to remain a mystery. But we have sufficient details to show that the region 
of Canada, Hudson’s Bay, and northwards to beyond the Arctic Circle, are under- 
lain by crystalline strata of this age, equally with the region of the United States 
to the southwards. 
(¢) General Result—Having thus shown that the continent of Europe on the 
one hand, and of North America on the other, has a solid framework and floor 
of crystalline stratified rocks, of presumably the same age, or approximately so, 
being in both cases pre-Cambrian or pre-Silurian, and assuming that these rocks 
* Dawson, ‘‘ Acadian Geology,” p. 662. 
| Logan, ‘‘ Geol. of Canada,” with Map. Dr. Selwyn estimates the area occupied by the beds 
forming the Archean nucleus at 2,000,000 square miles, ‘‘ Descriptive Sketch of the Geology of 
Canada,” p. 23 (1884). 
t “Manual of Geology,” p. 177. 
§ “U.S. Geol. Explor., 40th Parallel,” vol. i. pp. 17 and 58, &e. 
|| H. W. Fielden and C. HE. De Rance, ‘‘ Quart. Journ. Geol. Soc.,” vol, xxxiv. p. 556, 
