222 THE CANADIAN NATURALIST. [^'ol. vii. 



these plants took place during the deposition of the Erie clays, 

 ;and then judginii from the characteristic habits of the plants and 

 their range, and the distribution of the clays, that these clays 

 .are of marine origin. Circumstances also seem to favour the 

 x'lew that the Leda clays and Saxicava sands of the Ottawa and 

 St. Lawrence valleys were deposited about the same time. Mr. 

 -C- H. Hitchcock of Hanover, N.H., thinks that '• as Lake Supe- 

 Tior is 638 feet above the ocean, and the maritime plants surround 

 its shores, there is an argument for its submergence at least to 

 the depth of its surface, and probably to the height of its ter- 

 races, so that we may add 330 feet to the altitude of the lake. 

 This would give nearly 1000 feet, which corresponds well with 

 the knowu height at which marine shells have been found in 

 Arctic America, viz., one thousand feet on Cornwallisand Beechey 

 Islands.'' 



It seems most probable that the boreal and semi-Arctic plants 

 of the Lake Superior coasts, migrated thither contemporaneously 

 with or prior to the maritime plants. They are not now numer- 

 ous, but are of a marked northern type. They are not distri- 

 buted beyond the lake shores. It is only on the headlands which 

 iut far into the lake, and on the islands and the coast where the 

 bleak winds which sweep across and down the lake have full 

 play, and where the broad deep expanse of water keeps the atmos- 

 phere cool and moist, that they are met with. A few miles in- 

 land, beyond Fort William, the vegetation is in almost as great 

 profusion and is as rank as in the central districts of Ontario. 

 Even at the heads of deep bays on the northern coast, though in 

 R higher latitude, the plants are of a more temperate type than 

 those of Thunder Cape and other promontories. Upon some 

 headlands of the southern shores of the lake such boreal and 

 semi-aretic plants as Anemone parvijiora, Michx., jSuxi/raga 

 aizoides^ L., Sn.ri/r.igtf aizoon, Jacq., Saxifraya trieusjn- 

 da(a, Retz., 1\>I ijijuimiii vlcijxirmn, L., Empetriim nigrum, 

 Linu. and C<ire.c capillar'is, L., likewise occur, and though 

 it may, perhaps, be argued with apparent reason that the 

 presence of some of these may be due to the play of wind?:? and 

 currents from the northern and western sides of the lake, yet 

 there are others of these semi-arctic plants which have not yet 

 been seen on the upper coasts. Now if these northern species 

 here foria colonies isolated from their fellows to the far north, 

 without present means of communication, in accounting for their 



