BULL. GEOL. SOC. AM. 



VOL. 28, 1916, PL. 43 



,f 



I 



Figure 1. 



-Bedding in Slate Quaery, Upper Ordovician, Slatedale, Pennsylvani 

 rhotograph by H. S. Palmer. 1913 



Figure 2. — Ribboned Slate^ Upper Ordovician, Slatedale, Pennsylvania 



The ribbons have a dual division, consisting of carbonaceous mud below and fine-graine<l 

 sand above, emphasized by retouching the photograph 



UPPER ORDOVICIAN SLATE OF PENNSYLVANIA 



