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THE CLIMAX FOREST OF ISLE ROYALE, LAKE 
SUPERIOR, AND ITS DEVELOPMENT. III. 
CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY 165 
WILLIAM S. COOPER 
(WITH TWENTY-FIVE FIGURES) 
The hydrarch successions 
The bog succession 
I. Physiographic development of the bog habitat 
At the commencement of the glacial period the topography and 
the drainage system of what is now Isle Royale were very similar 
to those of today, except that lakes and swamps were few or absent. 
This topography was but slightly modified by the invasion of the 
ice, and the most important change effected by glacial erosion was 
the excavation of rock basins in the preglacial valleys. Since the 
retreat of the ice the gradual emergence of the island from the 
waters of the lake has taken place. In some cases inclosed basins 
appeared above the surface ready made; in others they were pro- 
duced by wave-built bars thrown across the mouths of harbors 
or both ends of channels during pauses in the retreat of the waters. 
By continued emergence some of these rock basins and cut-off bays 
came to occupy positions far in the interior of the island. The 
tilting which followed the Lake Nipissing stage must have had some 
effect upon the island lakes thus formed. It may have brought 
about the partial draining of some, the enlargement and perhaps 
even origination of others, and occasional shifting of outlets; in 
all cases it must have produced a tendency toward migration to the 
southwest. 
The physiographic development of the bog habitat thus includes 
as a rule two periods: first, the channel-bay stage, and second, the 
lake stage. Numerous localities that illustrate the process may be 
seen today, especially at the northeast end of the island. Duncan 
189] [Botanical Gazette, vol. 55 
