172 THE CAMBRIAN AND ORDOVICIAN DEPOSITS or MARYLAND 



Silurian has strong evidence in its favor. The present writer has had the 

 opportunity of studying the Richmond group over a large portion of the 

 United States with the result that in previous publications he has classi- 

 fied it at the base of the Silurian. . His treatement of the equivalent 

 Juniata formation in this volume under the Ordovician is not due to a 

 change of view, but to the fact that in the Silurian volume of the Mary- 

 land Geological Survey the base of the Silurian is placed at the Tuscarora 

 sandstone. As the Juniata is unfossiliferous and, moreover, is very poorly 

 exposed in Maryland, further details are believed unnecessary here, 

 and the reader is referred to the publication by Ulrich cited above for 

 more data as to its age. 



In Pennsylvania and Maryland the red sandstone and shales of the 

 Juniata formation form the upper slope of the mountains just west of the 

 Great Valley. These mountain slopes usually show only reddish sand- 

 stone blocks and it is only in cliffs or in road sections that the interbedded 

 red shales can be seen. The sandstone frequently shows cross bedding and 

 sometimes conglomerate beds of white quartz or red jasper boulders or 

 occasionally red shale pebbles are developed. The occurrences of the 

 formation in Maryland consists of small areas on Bear Pond Mountain, 

 a narrow strip on Fairview Mountain and another narrow strip along the 

 eastern side of Sword Mountain. None of these areas shows a section of 

 the rocks and the red shales and sandstones are known only from surface 

 debris. 



The relations and general characters of the Juniata and associated 

 formations are well shown in the following generalized section of Upper 

 Ordovician and Early Silurian strata made by E. 0. Ulrich and the 

 writer. This section is exposed along the west slope of Tuscarora Moun- 

 tain between McConnellsburg, Pennsylvania, and the summit of the 

 mountain, along the Mercersburg pike starting about a mile and a half 

 southeast of McConnellsburg and continuing southeast and south for 

 about two and one-half miles. 



