1913] COOPER—ISLE ROYALE 7 
small rock fragments mixed with organic matter. Most of these 
fragments are so decomposed that they can be cut easily with a 
knife. The bed rock itself frequently shows the effect of chemi- 
cal action. Vegetation is here seen as an important physiographic 
agent. 
Stream erosion is of trifling importance upon Isle Royale because 
of the small size and low gradient of most of the streams and their 
freedom from transported materials, necessary as agents of abrasion. 
Wave erosion is the most conspicuous of destructive agencies. 
The surf is actively cutting into the land, and the shore features at 
the present lake level are very pronounced. At many points along 
the southeast coast the normally gentle slope of the shore has been 
transformed into terrace and cliff. In some parts of the abrupt 
northwest shore the waves are undermining the climax forest itself. 
In connection with erosion by waves should be mentioned the work 
of ice, the precise effects of which could not be determined in sum- 
mer study. 
Under the head of CONSTRUCTIVE agencies come deposition 
by streams, waves, currents, and vegetation. The only notable 
instances of stream deposition are the few deltas, the materials for 
which were derived largely from the glacial drift and the products — 
of wave erosion at former levels. The subject is treated further 
under the head of “‘Delta swamp succession.” The fragments 
eroded by waves are deposited in the form of beaches and bars, 
in coves and harbors. Shore currents are effective in transporting 
the material, and in sweeping the finest into sheltered bays, where 
it is dropped in the quiet waters. The work of vegetation consists 
in the formation of peat and humus. Plant life here again appears 
as a physiographic agent of great importance. 
CLIMATE 
ADAMS (4, pp. 41-44) has described in some detail the climate 
of the general region, his data being obtained from the records of 
the Weather Bureau at Port Arthur. . The following summary 
(table I) is derived partly from ApAms’ account and partly from 
more recent data from Port Arthur obtained through the courtesy 
of the Canadian Weather Service. 
