1910.] NATURAL SCIENCES OF PHILADELPHIA. 543 



lacking in lime, potash or other desirable constituents. Hence the 

 soils derived from such rocks are naturally devoid of nutrient matter 

 and can support only a scanty growth of grass and stunted shrubs. 

 The main reason which may be assigned for their unproductiveness 

 is the large amount of magnesia which they contain and their slight 

 depth. The analyses of these soils show that they contain very 

 minute quantities of lime and phosphoric acid." 3 



The Conowingo Barrens are rarely, if ever, cultivated; even for 

 pasturage or for timber they are of little practical value. They have 

 thus remained very nearly in their original condition. On all sides, 

 however, they shade into the more tractable clay formation, which 

 is frequently cleared and cultivated. 



In Delaware and Chester Counties, as may be seen on the maps, 

 the Barrens lie in two main divisions : to the northeast they are small 

 and scattered (Chester Group), to the southwest they form essentially 

 one long continuous area (State-line Barrens). In the former are 

 some 10 or 12 well-marked exposures, ranging from less than one-half 

 acre (e.g., Sconnelltown) to such as the Serpentine Ridge, three to 

 four miles long. These areas lie near together in extreme southern 

 Montgomery, Delaware, southeastern Chester Counties, Pennsyl- 

 vania, and northwestern Newcastle County, Delaware. They are 

 separated some twenty miles from the nearest point of the State-line 

 Barrens. The latter extends as one ridge, some thirty-five miles long, 

 with a width of one to three miles, trending west-southwest from Little 

 Elk Creek, Chester County, Pennsylvania, through northern Cecil 

 County, Maryland, and over the Susquehanna River into Harford 

 County, Maryland. With this area are allied smaller side areas in 

 southern Lancaster County. Pennsylvania, near the Conowingo Creek. 



Most of the field-work of this study is concerned with the Chester 

 group of Barrens, practically every area of which in Delaware and 

 Chester Counties has been visited. The State-line Barrens have 

 been but twice visited, on both occasions in August, and the route 

 traversed from Nottingham Station to Goat Hill near Octoraro Creek. 

 As the barrens in this section are known as the Nottingham Barrens, 

 this more local name will be used in reporting specimens. 



The areas from which specimens have been examined are: 



3 C. W. Dorsey and J. A. Bonsteel, in Maryland Geol. Surv., Cecil Co. 

 Report, p. 237. 



