On the physical geography, geology, and commercial resources of Lake Superior / J.J. Bigsby.

  • John Jeremiah Bigsby
Date:
[1852]
Catalogue details

Licence: Public Domain Mark

Credit: On the physical geography, geology, and commercial resources of Lake Superior / J.J. Bigsby. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

    4/12 (page 157)
    ■Jp 1852.] OF THE ROYAL INSTITUTION. 157 is fire. (Large sketches were exhibited representing the lofty basaltic is country about Fort William, and the softer hill-scenery of Black !|l Bay.) s With the exception of the Fur trading stations, there are no white ill settlements on the north shore : — and this from its general bar- : iii renness. At the Peek River, soil was imported in bags with which is to raise a few potatoes. is The Fauna and Flora of Lake Superior are semi-arctic — or sub- is l alpine. Professor Agassiz has treated of both in his late valuable if publication on this lake. He found twenty-three new species of fish, st and states that Lake Superior constitutes a special ichthyological dis- trict. The reason of this evidently lies in the coldness and extreme I purity of the water, its slow departure towards the ocean, and the tl absence of weedy bays, and of lime rocks. It would seem that some portion of its animal life are waifs and k strays from grand geological periods long passed away — as we see in its herrings, minnows, and the new genus Percopsis. Connected s with this subject. Prof. Agassiz conjectures that much of North st America was dry land when the rest of the world was under water ; f, el and that thus its physical condition was less altered than elsewhere. • Dr. Bigshy was inclined to believe this, for had Canada been as long it under water as other large tracts, we should probably have had in 1, I some part of its vast extent, a member or two, at least, of the meso- it I zoic rocks ; but there is no such thing — not a single relic of lias, i oolite, or chalk, in the extraordinary heaps of debris which overspread ; these countries. Geology.* The rocks of Lake Superior have been arranged under ; ;! three principal heads, as follows : — 1. The Metamorphic.—Greenstone, chloritic, talcose, clay and greenstone slates, gneiss, quartzite, jasper, rock and saccha- roid limestone. 2. The Aqueous. — Calciferous sandstone, Cambrian sandstone and conglomerates. 3. The Igneous. — Granite, Sienite, Trap, in various states. The place and extent of these rocks having been pointed out on a map. Dr. Bigsby stated that the geological system of Lake Superior is a consistent and closely connected whole, forming a beautiful and li easily read example of geological action in moulding the surface of ill our globe. The lake may best be presented at once to the mind as a trough or basin of Cambrian (or Silurian) sandstone, surrounded, and framed as it were, by two orders of rocks, in the form of irregular ■ and imperfect zones; the inner consisting of trap, with its conglo- >: merates; and the outer, of metamorphic, flanking igneous rocks. * This branch of the subject was illustrated by numerous coloured Diagrams, and specimens of native copper, and of the rocks of the lake.