ECOLOGY OP ISLE ROYALB. 45 



•stream. Foster and Whitney ('50, p. 51) make the following comment 

 upon these fluctuations at Rock Harbor; "While at Rock Harbor, Isle 

 Royale, in the summer of 1847, we witnessed the ebbing and flowing of 

 the water, recurring at intervals of fifteen or twenty minutes, during; 

 the entire afternoon. The variation was from twelve to eighteen inches ; 

 and we took advantage of their recession to catch some of the small 

 lake fish which were left in the pools. The day was calm and clear 

 l)ut before the expiration of forty-eight hours a violent gale set in." 



This phenomenon has been investigated on the Great Lakes by Deni- 

 son ('98, p. 568) who states that these seiche movements are very 

 marked preceding and during storms and are due to atmospheric pres-. 

 sure upon the lake. 



c. Climatic Succession. From what is known of the general geologi- 

 cal history of the Superior region, during Glacial and post-Glacial times, 

 it is evident that there has been a great climatic change which has been 

 •of the utmost biological importance. It is therefore desirable to see 

 what inferences will aid us in forming a general conception of the pos- 

 ■sible climatic successions. It appears to be generally conceded that at the 

 margin of the ice sheet the conditions must have been quite arctic in 

 character, similar to that of the "barren grounds" of the far north. Such 

 climatic conditions might result from a permanent atmospheric low cor- 

 related with the presence of the ice sheet (Cf. Chamberlin and Salisbury, 

 '06, 11, pp. 674-675 ; 111, p. 43E) . The prevailing westerlies, combined with 

 a permanent Ioaa^^ to the north would favor westerly continental winds 

 along the margin of the ice. Perhaps a suggestive comparison can be 

 made between tlie seasonal transitions from the two permanent winter 

 lows near the Arctic regions, into the summer condition of one low with 

 its transitional "March weather" and that of American and European 

 glacial lows and their transformation into the present summer arctic 

 low. In connection with this subject a paper by Fassig ('99) is of spec 

 ial interest. Analogies are often dangerous but the idea is of interest 

 Tiecause it suggests a "March weather" transformation for post-Glacial 

 times. In this connection the formation and occurrence of the wind 

 blown loess, with its greatest development in the west and on the east 

 banks of certain streams, is of special interest, although these condi- 

 tions did not develop in .the north as they did farther south. The oc- 

 ■currence of the westerly winds seems to be further supported by the west- 

 erly and southwesterly extension of the ice from the centers of the accum- 

 ulation (Cf. Chamberliii and Salisbury, '06, 111, pp. 330-333). Some- 

 Tvhat similar conditions in some respects obtained in Europe (Penck, '06, 

 p. 183). but the dry winds were eastejly rather than westerly as in North 

 America. The European loess deposits also approached much nearer 

 to the (western Europe) coast than in America, where they remain far 

 to the interior. The Great Lake storm track may have been wider, but, 

 more probably, was narrower and more intense. The northeastward re- 

 treat of the ice sheet is paralleled by the northeastward migration of 

 spring weather conditions (Bigelow, '97, p. 48) and if this route of the 

 opening of spring was initiated at- this early date it must have had 

 important biological consequences upon the migrating animal life of the 

 interior. The arctic and storm track types of climate are perhaps the 

 only ones which Isle Royale has possessed, although the storm centers 



