512 proceedings of the academy of [oct., 



Physiography axd Soil. 



The Conowingo, or Serpentine, Barrens occur as small isolated 

 areas, stretching in a much broken chain near the coastward edge of 

 the Piedmont Plateau from New England to North Carolina. In 

 Pennsylvania they lie in a hilly, much eroded country, and, owing to 

 the chemical stability of serpentine rock, occur usually on crests and 

 as low ridges. 



Their geologic structure is striking and has been frequently de- 

 scribed. 1 Their soil has been lately described in several publications 

 of the Division of Soils of the U. S. Department of Agriculture. 2 In 

 these the name Conowingo Barrens is consistently applied, which 

 has led to its adoption in the present paper. 



Two types of soil are derived from the weathering of the Serpentine 

 — itself a soft, green, altered igneous rock: the Conowingo Barrens 

 and the Conowingo clay. ( )f these the latter represents a much decom- 

 posed soil of considerable depth and forms a transition between the 

 Conowingo Barrens. and the normal mellow soils of the district. The 

 Conowingo Barrens are alone considered here. 



"The soil (of the Conowingo Barrens) generally is a light yellow 

 or whitish-looking loam, but in places it is almost black. The top 

 soil occasionally has a depth of 8 or 10 inches, and it is underlain by a 

 yellowish-brown subsoil to. a depth of 36 inches. The soil is generally 

 much shallower, and in the case of the barren hills of this formation 

 the rocks are devoid of any trace of soil covering except that caught 

 in the pockets and crevices of the rocks. Frequently even on level 

 or lightly rolling areas the soil may not exceed a few inches in depth. 

 These soils, as seen from the mechanical analyses of samples collected, 

 are not essentially different from man}' of the productive upland 

 soils, but they are unproductive, and in extreme cases will not produce 

 anything in a natural state except a stunted growth of small pines 

 and knotty oak trees. At the best they are stubborn and unproduct- 

 ive, and although many reasons have been assigned for their sterility 

 none seem altogether satisfactory. Professor Merrill (Rocks, Eock- 

 weathering, and Soils. 1897) in speaking of the Chester County Barrens 

 says that these soils are derived from the slow decomposition of 

 peridotites, rocks rich in iron-magnesium silicates, but almost wholly 



1 See (a) Maryland Geol. Survey, Cecil Co. Report; (6) Penna. 2d Geol. 

 Surv., Chester Co. Report; (c) Philadelphia Geol. Folio, 1909. 



-See (a) Man/land Geol. Survey, Cecil Co. Report; (b) Harford Co. Report 

 (c) U. S. Div. of Soils, Chester Co., Penna., Report. 



