98 J. E. CRIBBS 



former of these regions occupies a zone extending from a point 

 approximately forty miles north of Pittsburg, northward to 

 Lake Erie. It is about thirty miles wide in the central part and 

 gradually diverges northward, following very closely the course 

 of the Allegheny River. The topography is of a rolling morainic 

 character, and the soil a mixture of glacial boulder clays. The 

 latter region borders this on the east, and extends eastward 

 to the Allegheny Mountains, forming the Allegheny Plateau. 

 The soil here is predominantly of yellow clay and the topography 

 very much broken up into rough, irregular, hills and valleys. 

 The altitude of the glaciated region ranges from 573 feet at Lake 

 Erie to 1350 feet in Mercer County, while that of the unglaciated 

 area extends from about 715 feet at Pittsburgh to 1840 feet in 

 southern Warren County. 



The following climatic data, compiled from Grove City Col- 

 lege records, is worthy of notice since it bears a direct relation 

 to the type of flora developed there as a climax. The table 

 below shows the average rainfall during the months of April to 

 November inclusive. This is the period of the year during 

 which the soil is not frozen and hence retains large quantities of 

 water which become available for vegetative growth. • 



inches inches 



April 4.12 August 3.61 



May 3.60 September 3.91 



June 3.52 October 3.03 



July 4.73 November 2.05 



The average annual rainfall is 41.7 inches. 

 The average rainfall for above eight months — 28.63 inches. 

 The average annua' snowfall is 58.26 inches. 

 The following average temperatures are given for the months 

 during which the greatest vegetative development occurs. 



April 49.53°F. August.? 67.10°F. 



May 57.40° F. September 63.60° F. 



June 67.70° F. October 51.65° F. 



July 70.00° F. 



The average temperature for these seven months is seen to 

 be 61°, while that of the five months of comparative inactivity 



