THE HURONIAN PERIOD.

The so-called Huronian Rocks, like the Laurentian, have their typical development in Canada, and derive their name from the fact that they occupy an extensive area on the borders of Lake Huron.  They are wholly metamorphic, and consist principally of altered sandstones or quartzites, siliceous, felspathic, or talcose slates, conglomerates, and limestones.  They are largely developed on the north shore of Lake Superior, and give rise to a broken and hilly country, very like that occupied by the Laurentians, with an abundance of timber, but rarely with sufficient soil of good quality for agricultural purposes.  They are, however, largely intersected by mineral veins, containing silver, gold, and other metals, and they will ultimately doubtless yield a rich harvest to the miner.  The Huronian Rocks have been identified, with greater or less certainty, in other parts of North America, and also in the Old World.

The total thickness of the Huronian Rocks in Canada is estimated as being not less than 18,000 feet, but there is considerable doubt as to their precise geological position.  In their typical area they rest unconformably on the edges of strata of Lower Laurentian age; but they have never been seen in direct contact with the Upper Laurentian, and their exact relations to this series are therefore doubtful.  It is thus open to question whether the Huronian Rocks constitute a distinct formation, to be intercalated in point of time between the Laurentian and the Cambrian groups; or whether, rather, they should not be considered as the metamorphosed representatives of the Lower Cambrian Rocks of other regions.

As regards the fossils of the Huronian Rocks, little can be said.  Some of the specimens of Eozooen Canadense which have been discovered in Canada are thought to come from rocks which are probably of Huronian age.  In Bavaria, Dr Guembel has described a species of Eozooen under the name of Eozooen Bavaricum, from certain metamorphic limestones which he refers to the Huronian formation.  Lastly, the late Mr Billings described, from rocks in Newfoundland apparently referable to the Huronian, certain problematical limpet-shaped fossils, to which he gave the name of Aspidella.

LITERATURE.

Amongst the works and memoirs which the student may consult with regard to the Laurentian and Huronian deposits may be mentioned the following:[10]—­

(1) ’Report of Progress of the Geological Survey of Canada from its
    Commencement to 1863,’ pp. 38-49, and pp. 50-66.
(2) ‘Manual of Geology.’  Dana. 2d Ed. 1875.
(3) ‘The Dawn of Life.’  J. W, Dawson. 1876.
(4) “On the Occurrence of Organic Remains in the Laurentian Rocks
    of Canada.”  Sir W. E. Logan.  ‘Quart.  Journ.  Geol.  Soc.,’
    xxi. 45-50.’