ILLUSTRATIONS 



PLATE FACING PAQB 



I. Map showing the Distribution of the Cambrian and Ordovician 



Deposits of Maryland , . 23 



II. View of the Potomac Water Gap at Harper's Ferry 52 



III. Fig. 1. View of the Great Valley from South Mountain at Blue 



Mountain Station 56 



Fig. 2. View along road between Pen Mar and High Rock, Mary- 

 land, showing mountain side covered with blocks of Weverton 

 quartzite 56 



IV. Fig. 1. Exposure of Tomstown limestone along trolley line just 



southeast of Wagner's Cross Road, Washington County, Mary- 

 land, illustrating weathering of massive sheared limestone 

 into shale fragments 62 



Fig. 2. Limestone quarry at Cavetown, Maryland, showing Toms- 

 town limestone faulted against Waynesboro sandstone 62 



V. Fig. 1. Valley of Tomstown limestone looking east from Cave- 

 town, Maryland, showing foothills of Harpers shale, and 

 South Mountain of Weverton sandstone in the distance 64 



Fig. 2. Valley of Tomstown limestone with South Mountain in 

 the distance showing peneplained surface. The hill just 

 beyond the house is capped by Tomstown chert. Photograph 



taken one mile south of Cavetown, Maryland 64 



VI. Fig. 1. Overturned fold with slight faulting in Tomstown lime- 

 stone along Western Maryland Railway, one mile west of 

 Cavetown, Maryland 66 



Fig. 2. Ridge of the Waynesboro formation just east of Middle 



Bridge, Antietam Battlefield, Washington County, Maryland . . 66 

 VII. Iron stained contorted sandstone of Waynesboro formation. The 

 upper figure represents the usual aspect of the rock. The 

 cavities in the sandstone are covered by drusy quartz as 

 shown in the figure to the left (x2) or by beautiful minute 



crystals of quartz illustrated in figure to right (x 6) 68 



VIII. Fig. 1. Exposure of Elbrook limestone along Baltimore and Ohio 

 Railroad just south of Sharman, Maryland. These massive 

 beds weather into thin shaly layers 72 



Fig. 2. View looking north over Antietam Battlefield showing 

 exposure of Elbrook limestone. Photograph taken one-half 

 mile east of Sharpsburg, along road to Burnside Bridge, 

 Maryland 72 



