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Show 226 DELTA OF LAK~ SUPERIOR. other Canadian lakes, leading us to infer that its waters have formerly occupied a much higher level than they reach at present; for at a considerable distance from the present shores, parallel lines of rolled stones and shells are seen rising one above the other, like the seats of an amphitheatre. These ancient lines of shingle are exactly similar to the present beaches in most bays, and they often attain an elevation of forty or fifty feet above the present level. As the heaviest gales of wind do not raise the waters more than three or four feet ~, the elevated beaches must either be referred to the subsidence of the lake at former periods, in consequence of the wearing down of its barrier, or to the upraising of the shores by earthquakes, like those which have produced similar phenomena on the coast of Chili. But there seem to be no facts which lend countenance to the latter hypothesis, in reference to the North American lakes. The streams which discharge their waters into Lake Superior are several hundred in number, without reckoning those of smaller size; and the quantity of water supplied by them is many times greater than that discharge<l at the Falls of St. Mary, the only outlet. The evaporation, therefore, is very great, and such as might be expected from so vast an extent of surface. On the northern side, which is encircled by primary mountains, the rivers sweep in many large boulders with smaller gravel and sand, chiefly composed of granitic and trap rocks. There are also currents in the lake, in various directions, caused by the continued prevalence of strong winds, and to their influence we may attribute the diffusion of finer mud far and wide over great areas; for, by numerous soundings made during the late survey, it was ascertained that the bottom consists generally of a very adhesive clay, containing. shells of the species at present existing in the lake. When exposed to the air, this clay immediately becomes indurated in so great a degree, as to require a smart blow to break it. It effervesces slightly with diluted nitric acid, and is of different colours in different parts of the lake ; in one district blue, in another red, and in a third • Captain Bayfield remar~s, that Dr. Bigsby, to whom we are indebted for several communications respecting the geology of the Canadian lakes, was misinformed. by th~ fur traders in regard to the extraordinary height.(twenty or thirtyf~t) towh1ch he asserts that the autumnal gales will raise the water of Lake Super10r. Trans, of Lit. and Hist. Soc. of Quebec, vol. i., p. 7, 1829. DELTAS OF TilE BALTIC . 227 white, hardening into a substan ee resembltn. O' · 1 these statements, the geolo ist .11 o pipe-c ay ~A<. From these recent lacustrine for~ati:~s ?:t fail t? rema~k how closely tiary argillaceous and calcare fmerzca rese.mble the tcrCentral France. In b th ous mar s of lacustrme origin in o cases many of th most abundant, as Lymnea and PJ . e genera of shells in regard to other classes of or . anorb~s, are the same; and closest analogy, as we shall gdamc remams, there must be the h . en eavour more fi 11 . w en speakmg of the imbeddin f 1 ~ Y to explam deposits. g 0 P ants and ammals in recent DELTAS OF INLAND SEAS. Deltas of the Baltic.-HavinO' offi d lacustrine deltas now in P 0 ere these few remarks on . rogress we may n t t twTn to those of inland se ' ex urn our at ten- as. he shallowing and conversion into 1 the Baltic, especially the Gulf: f B h ~nd of many parts of been demonstrated by a se . fs o ot ma and Finland, have rzes o accurate obs t · .1! we .are in a great measure indebted to :rva Ions, JOr which which has been kept up . h . the ammated controversy conc~rning the gradual' l::~~i~O'e middle of the last century' Celszus, the Swedish astronomer o of th~ ~evel of the Baltic. from the earliest times there had b first orzgmate.d the idea that forty-five inches in a centur in ;~n a progressive fall of about of that sea. He contended ~b t th'e mean level of the waters modern observations but tha Ishch~nge rested not only on g h ' on e aut onty of th . rap ers, who stated that S d' . e anCient geo- By the gradual depression o~a~l:~::zah was. formerly an i~land. became connected with th . ' e said, that great Island d f e contment . and th t h' pene a ter the time f Pl' ' a t 1s event hap-our era. To the a o my, and. before the ninth century of 1 . rguments urged 111 sup t f h us opponents objected th t tl . por o . t ese positions geography of the most a t~e .ancients were so ignorant of th~ authority was entitled t nor ei~ parts of Europe, that their tation of Scandi . o no. weight; and that their represen-be ad d uced to pnroa via tahs an Isla.n d ' m.I g ht W.i t h more propriety to confirm so bold :: h e o~can~mess of their information, than the land which YP hesis. It was also remarked that if connected Scandinavia with the mru.'n con tm' ent * Trans. of Lit a d H' t , n IS ' Soc. of Quebec, vol. i., P• 5, 1829. Q~ |
