An associational study of Illinois sand prairie . oclea, the lizards tail, Saururus, and others. Northern in-sects such as Corymbites pyrahos have also been taken. The old bot-tom of the Mackinaw river is filled with peat, and the broad levelareas were entirely grovra over with swamp vegetation. From that timeto the present, changes in the vegetation in the level areas and inthe ridres have represented entirely distinct orders of succession. The arid v/hich accompanied the retreat of the glacierswas at about this time gradually changed, the rainfall was materiallyincreased, and the te
An associational study of Illinois sand prairie . oclea, the lizards tail, Saururus, and others. Northern in-sects such as Corymbites pyrahos have also been taken. The old bot-tom of the Mackinaw river is filled with peat, and the broad levelareas were entirely grovra over with swamp vegetation. From that timeto the present, changes in the vegetation in the level areas and inthe ridres have represented entirely distinct orders of succession. The arid v/hich accompanied the retreat of the glacierswas at about this time gradually changed, the rainfall was materiallyincreased, and the temperature became probably somewhat cooler. Itis an unpublished opinion of Professor Gleason that the eastern, orprairie-grass formation, had not developed before the change in climaand that this gradual change favored the evolution of a mesophytictype of prairie, over the whole eastern extent of the province. Theuplands on both sides of the river, surrounding the sand-plain, weresoon covered v;ith this black-soil prairie, to the exclusion of the. 31 older xerophytic type, which was, however, preserved with little or no change, on the sand ridges. At the same time, or a little later, hydrophytic raembers of the same sweimp-prairie association appeared the on the sandy loeun flat and began to compete withyy^northern bog type,which gradually gave way to its western rival, except in a few lo-calities unfavorable to the invaders. Another far reaching effect of the increase of rainfall and hu-midity was the spread westward and northward of the deciduous forest, probably v;hich during the and period was ^developed only a short distancenorth of the Ohio River. The northern migration in the eastern states(Adams, 1905) was aided materially by a northward moving wave oftemperature increase, which followed the retreat of the extension of the forest to the north and west is evidently stillin progress, though it is obscured by t-^e clearing of land for agri-culture. In the Hav
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Keywords: ., bookcentury1900, bookdecade1910, bookidassocia, booksubjecttheses
