20 , 



William S. Cooper then gave an illustrated paper of which 

 the following is an abstract. 



PRELIMINARY ACCOUNT OF THE FOREST SUCCES- 

 SIONS ON ISLE ROYAL, LAKE SUPERIOR. 



Isle Royal, an island near the northwest shore of Lake Su- 

 perior, is fifty miles long and six to ten miles wide. Its topog- 

 raphy is determined by a parallel series of tilted beds of 

 Keweenawan and Cambrian age, which dip southeast under Lake 

 Superior. The result of. this structure is a series of ridges 

 extending northeast and southwest, parallel to the long axis 

 of the island, with steep faces on the northwest, but sloping 

 gently to the southeast. The ridges bound long narrow valleys 

 which contain bogs and lakes, or harbors if below the present 

 lake level. 



The island was overridden by the continental glacier, and 

 on the retreat of the ice was left entirely submerged beneath 

 the waters of Lake Diiluth. As the lake level subsided the is- 

 land gradually emerged, finally reaching its present size. It 

 has never been connected with the mainland since glacial 

 times. 



The dominant forest of the island is composed of white 

 spruce, paper birch, and balsam fir. Whether this is the climax 

 forest toward which the earlier successional stages tend cannot 

 be determined at present. The uncertainty is due to two causes: 

 the presence on the southwestern end of a well developed forest 

 of sugar maple, which is the most important tree of the climax 

 forest farther south ; and the apparently unstable character of 

 the dominant forest. It can be said with certainty, however, 

 that the successional stages lead to the spruce-birch-balsam 

 forest. Whether this in turn will tend to become maple forest 

 is the doubtful point. 



The devil's club (Patsia horrida), first discovered on the 

 island by W. A. Wheeler, was found in four isolated localities 

 in the forest at the northeast end. It is a very common plant 

 in the western mountains and is known nowhere in the east 

 except on Isle Royal. 



