126 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND 



This fauna is correlated with the Middle Chazy or Crown Point lime- 

 stone of New York and the Lenoir limestone of southern Virginia and 

 Tennessee, in each of which most of these species occur. 



Upper Stones River. The upper division consists of very pure, thin- 

 bedded, dove-colored or pearl gray homogeneous limestone which is quite 

 frequently exposed because most of the quarries are in this rock. The 

 large quarry at Pinesburg Station exposes a considerable thickness of 

 these pure upper beds. Here also sections of numerous fossils may be 

 noted, but the rock is so homogeneous that the specimens cannot be 

 broken out, and it weathers in such a manner that the fossils are not left 

 in relief on the surface. The only species which can be obtained in any 

 fair state of preservation is the characteristic. Stones River single tube 

 coral Tetradium syringoporoides. 



A conspicuous topographical feature of this portion of the Stones 

 River particularly is the occurrence of numerous sinks along its line of 

 outcrop. However, conditions favoring the formations of such sinks 

 occur also in the lower portion of the Stones River. 



AREAL DISTRIBUTION AND TOPOGRAPHIC FORM. The outcrops of the 

 Stones River limestone in Maryland are confined to the Appalachian 

 Valley and cross the state in five distinct bands, three of which occur east 

 of the shale belt of the middle portion of the Valley, and two to the west. 

 The strata of the three eastern belts are not as highly folded as those to 

 the west and the areas of outcrop are therefore wider. Each of these 

 belts occupies a nearly level lowland broken only by low hills formed by 

 the cherty middle division. In the northern half of these three belts the 

 chert and resulting low hills of the Middle Stones River are especially 

 well developed. In Maryland this middle portion has been noted in out- 

 crops at many points. The residual black chert is frequently so abundant 

 in the soil that it leaves its impress upon the topography in the form of 

 low hills arranged according to the geological structure. This is illus- 

 trated in an area just south of the Pennsylvania state line and directly 

 north of Hagerstown where the outcrop of the Middle Stones River 

 cherty limestone is plainly indicated by the low hills elongated in a 



