, MARKINGS IN PENNSYLVANIAN SANDSTONES 69 
Fic. 1.—Block of sandstone 53 feet in height showing parallel strand markings 
on a bedding plane. This is the lower surface of the bed and the markings are casts 
of the original. As shown by the ruler in one of the upper grooves, the coarser mark- 
ings are grooves in this cast. The relief of the surface is less than 1 inch. Locality, 
S.E. cor., N.E. {, Sec. 8, T. 20 N., R. 12 E., Osage County, Oklahoma. Photo by 
Lucian Walker, of Tulsa, Oklahoma. 
Fic. 2.—Another block of sandstone at the same locality as Figure 1, showing 
a curve in parallel markings, and also showing irregular markings which are depressions 
in the cast. Nothing but flexible objects such as fronds of algae could have produced 
@ curve in some of the markings and not in others when dragged along the strand. 
The irregular markings near the top may be casts of stranded algae. Photo by 
R. H. Wood, United States Geological Survey. 
