54 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND 



lost by metamorphism during the folding of the rocks. The Loudon slate 

 can be f ouncl at localities one mile east of Harper's Ferry and half a mile 

 south of Rohrersville, Maryland, with coarse fragments of the Catoctin 

 schist such as epidote and jasper imbedded in it. 



The conglomerates of the Loudon formation, with few exceptions, are 

 confined to the synclinal areas where the Weverton sandstone is not 

 present. These conglomerates are limited in extent and are composed of 

 quartz, granite, jasper, and epidote boulders imbedded in the usual black 

 slate. Grains of magnetite and ilmenite washed from the Catoctin schist 

 are present in many of the beds. Sandstones likewise occur, but these are 

 thin and unimportant in Maryland, their greatest development being 

 south of the Potomac River. 



The Loudon formation as a whole has been subjected to much meta- 

 morphism and its various members exhibit the usual metamorphic prod- 

 ucts, namely, quartzite, slate, schist, and marble. The alteration is most 

 marked in the argillaceous beds where all trace of their original stratifica- 

 tion has been lost in the change to slate and schist. This slate and the 

 few marble areas weather readily, forming low ground. The more 

 siliceous rocks, metamorphosed into quartzite, resist weathering and as a 

 result form the low hills or ridges of the Loudon areas. 



No fossils have been discovered in the Loudon formation, the conditions 

 of sedimentation being unfavorable for the preservation of organic re- 

 mains. These rocks, however, apparently mark the beginning of the 

 siliceous Lower Cambrian deposits, the age of which is determined by 

 paleontological evidence in the overlying Harpers shale and Antietam 

 sandstone. 



THE WEVERTON SANDSTONE 



The prominent outcrops in the gorge of the Potomac River at the south 

 end of South Mountain near Weverton, Maryland, consist of massive beds 

 of fine, pure, white and purple sandstone, quartzite, and conglomerate, 

 overlying the basal Cambrian Loudon formation. These strata, termed 

 the Weverton sandstone, are the most resistant of all the Cambrian and 

 Ordovician deposits, and for that reason they are the main mountain- 



