MARYLAND GEOLOGICAL SURVEY 237 



areas are of some size, but the others contain only a few acres. The 

 largest of these areas begins at the Susquehanna, a half mile north 

 of Conowingo, and continues northeast to the Pennsylvania boundary. 

 The other areas are situated near by. All of the areas of this forma- 

 tion are rough and hilly. Conowingo and Octoraro creeks now 

 through both areas, which accounts for the rough and broken surface 

 of the country. 



This soil is derived from the weathering of serpentine, which is an 

 altered eruptive rock of a dark greenish color. The soil 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 

 is underlain by a yellowish-brown loam 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 covering may not exceed a few inches in depth. These soils, 

 as seen from the mechanical analyses of samples collected, are not 

 essentially different from many of the productive upland soils; but 

 they are unproductive, and in extreme cases will not produce any- 

 thing in a natural state except a stunted growth of small pines and 

 knotty oak trees. At the best, they are stubborn and unproductive, 

 and although many reasons have been assigned for their sterility, 

 none seem altogether satisfactory. Professor Merrill, 1 in speaking 

 of the Chester county barrens, just across the State line in Pennsyl- 

 vania, says that these soils are derived from the slow decomposition 

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

 wholly 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 percentage of magnesia which they 

 contain, and their slight depth. The analyses of these soils show 



1 Rocks, Rock-weathering, and Soils, 1897. 



