184 LAKE SUPERIOR. 



that but a few dwarfish Red Oaks are seen in the Island of Michipi- 

 cotin ; but the Elm is still handsome about Fort William, though it is 



7 O 



very scarce in other parts of the northern shores. 



The shores of Nipigon Bay, the northernmost point we visited, are 

 covered with Pine forests, with a few Ashes and Maples, and here and 

 there a Sorbus americana among them. At this latitude, the 49, 

 we had therefore not yet reached the zone of the true alpine vegeta- 

 tion, and remained for the whole extent of our journey within the 

 limits of the sub-alpine flora. 



The highest point which we visited, the summit of a mountain upon 

 St. Ignace Island, which we called Mount-Cambridge, afforded the 

 following harvest for our herbarium : Abies balsamea, Abies alba, 

 Betula papyracea, Alnus viridis, Sorbus americana, Amelanchier 

 canadensis, Acer montanum, Diervillea trifida, Sambucus pubens, 

 Rhus Toxicodendrum, Vaccinium uliginosum, Corylus rostrata, Lin- 

 naea borealis, Cornus canadensis, Spiraea opulifolia, Salix, Cory- 

 dalis glauca, Epilobium angustifolium, Polygonum ciliare, Melam- 

 pyrurn, Clintonia borealis, Stereocaulon paschale, Gyrophora hirsuta, 

 Cladonia pyxidata, and rangiferina, Parmelia tiliacea and Sphagnum 

 acutifolium. 



From this list it is obvious, that even a thousand feet of height 

 will introduce very slight differences in the vegetation of these re- 

 gions. For, though Mount Cambridge is about a thousand feet above 

 the level of the lake, its whole slope is covered with the same vege- 

 tation which occurs at the very level of the lake. 



This fact would seem in flat contradiction with the general laws of 

 the geographical distribution of plants, to which we have alluded above, 

 but for the presence of the lake itself and its peculiar character. 



So large a sheet of so deep water as Lake Superior, preserving all 

 the year round a very equable and low temperature even on its 

 shores, which are generally very precipitous, must of course influence 

 greatly the temperature of the main land in its immediate vicinity, at 

 considerable heights above its surface. 



There is, therefore, nothing very surprising in our finding so uniform 

 a vegetation at rather considerable heights above the surface of the 

 lake and on its immediate shores. 



This fact is to be attributed to the equalizing local influence of the 



