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each case examined the portion of the river valley from which 

 the forests have been removed is shallow and without prominent 

 bluffs, while those portions in which the forests are still standing 

 show more pronounced effects of erosion. The bluffs and ravines 

 of these more rugged valleys have doubtless been of great impor- 

 tance in protecting the forests from the fires. 



Some of these isolated groves are still in a pioneer condition, 

 with oaks as the chief or sole component of the forest, as in Bur 

 Oak Grove, described in an earlier paper. Others had reached 

 a climax stage before the fires separated them from the main body 

 of the forest, and contain such typical mesophytes as Acer 

 Saccharum, Tilia americana, Quercus Muhlenhergii, and Cercis 

 canadensis. This is especially true of Big Grove, adjacent to 

 the city of Urbana in Champaign County. Those groves 

 farthest up stream are usually especially characterized by Quercus 

 veliitina, Quercus imbricaria, or other similar xerophytes. 



In some cases, also, the stream valley between the isolated 

 grove and the main body of forest has in recent times grown up 

 to a narrow fringe of trees, in which Ulmus americana is usually 

 most abundant. 



II. There are two groves in Champaign County of such 

 peculiar nature that only recently a satisfactory explanation 

 for them has been obtained. These are Mink Grove, situated 

 just west of Rantoul, and easily visible from the Illinois Central 

 Railway, and Linn Grove, four miles southeast of Philo. Their 

 most remarkable feature is the complete absence of the genus 

 Quercus, a phenomenon which probably could not be duplicated 

 in any other forest area of equal extent in the state. Mink 

 Grove, the smaller of the two, is located on a low morainic hill, 

 surrounded on three sides by low ground. Before drainage this 

 slough was usually full of standing water and was marked on the 

 original survey (with some slight errors of shape) as a lake. 

 Obviously it was easily protected from fire. The nearest forest at 

 the present time is about six miles away. The characteristic 

 trees are Carya cordiformis , Gleditsia triacanthos, Ulmus ameri- 

 cana, Ulmus fidva, Primus serotina, Juglans nigra, Celtis occiden- 

 talis, Morus rubra, and Crataegus sp. Of these nine species four 



