MARYLAND GEOLOGICAL SURVEY f>9 



percentage of carbonate of lime. Its color is usually white, but some of 

 the upper layers change to a dull brown. Actual outcrops of the rock are 

 very rare, but its presence can be determined readily by the numerous 

 lumps of white sandstone strewing the surface and by its topographic 

 form. On account of their location and the abundance of rock fragments 

 in the soil, its areas of outcrop are unsuitable for agriculture other than 

 the growth of fruit trees. 



The Antietam sandstone does not outcrop in a continuous belt like the 

 associated formations, but is displayed in a number of small areas just 

 west of the main elevation of South Mountain. Its occurrence coincides 

 with that of the Harpers shale, and indeed Keith's detailed mapping has 

 shown that this sandstone is found only as synclinal remnants lying upon 

 the shale. The largest of these areas in Maryland are the ridge about 

 four miles long just east of Ponds ville and the V-shaped ridge east of 

 Mapleville. The elevation just east of Boonsboro likewise is composed 

 of Antietam sandstone, while a few small areas are infolded in the 

 Harpers shale belt just north of Eohrersville. The western foot hills of 

 Elk Ridge likewise contain a few small, scattered areas, while the larger 

 elevation two miles east of Sharpsburg is composed almost entirely of 

 this formation. The Harpers shale belt on the east side of Catoctin 

 Mountain contains small, schistose, sandy beds lying above the Harpers 

 shale which may be the metamorphosed equivalent of the Antietam sand- 

 stone. 



Except a few worm burrows in the sandstone member of the Harpers 

 shale, the Lower Cambrian deposits in Maryland are practically un- 

 fossiliferous beneath the upper part of the Antietam sandstone. Even 

 here fossils are by no means common at any place. In Maryland the best 

 locality for fossils is in the sandstones along the mountain front near 

 Eakles Mills where fragments of Olenellus thompsoni Hall, Hyolithes 

 communis Billings, and Obolella minor Walcott have been found by Wal- 

 cott. These fossils are associated with the Scolithus tubes which are 

 abundant in the upper part of the formation at practically all of its out- 

 crops. This fauna, although small, is sufficient to determine the age of 



