PAPERS ON BOTANY 117 



So far as I have been able to see, nothing very peculiar 

 marks the ecological occurrence of Quercus ellipsoidalis. 

 Its associates where I have found it in Illinois are the 

 usual components of groves in the northern part of the 

 State, and there is no evidence that it is influenced by 

 them or influences them materially. As has been stated 

 already, its distribution has not been connected either 

 with evident barriers, drainage systems, or particular 

 superficial glacial deposits. On the other hand, the south- 

 ern limit of its occurrence in the State coincides in general 

 with the southern limit of underlying geological strata 

 older than the Carboniferous, and its entire known distri- 

 bution falls in Silurian, Ordovician and Cambrian regions : 

 but in eastern Illinois it does not reach the southern limits 

 of the Silurian. I have no knowledge of its occurrence 

 over these older rocks to the southeast of the Lake, for it 

 is reported for Lake County, Indiana, only, and, so far as I 

 know, is not found in western Ohio, which is of similar 

 geologic age. 



The absence of the jack oak from this part of the ad- 

 jacent older formations requires separate consideration, 

 though its explanation may perhaps be sought in the vary- 

 ing chemical composition of the soil through the territory 

 covered by these older outcroppings ; but the failure of the 

 tree to penetrate the Carboniferous territory, which consti- 

 tutes the larger part of Illinois, apparently bears a very 

 close connection with , the circumstance brought to my 

 attention by my former colleague, Dr. J. L. Rich, that the 

 glacial drift which overlies local rocks in this region may 

 be all but exclusively derived from rock of the immediately 

 adjacent country.* If this conclusion be correct, the 

 peculiar and abrupt ending of the range of the jack oak 

 in Illinois may be due primarily to its intolerance of the 

 iron, sulphur, magnesium, etc., with which the rocks of the 

 coal country are charged and the presence of wliich is very 

 evident in the water of this region. 



*Alden, Professional Paper, U. S. Geol. Survey. 34:75, 

 1904.— In a very extensive study of the soils of southern 

 Wisconsin, though only 50 per cent of the drift materials 

 were found to be of local origin in one case, the general 

 local constituents comprised between 68 and 97 per cent in 



