MARKINGS IN PENNSYLVANIAN SANDSTONES 72 
Irregular markings, mostly grooves in the casts, are character- 
istic of many slabs of sandstone associated with the parallel mark- 
ings. In Figure 3 they have the appearance of being made by 
objects swept back and forth on the strand while suspended from 
One or more common centers. Still more irregular markings 
(Fig. 5), all depressions on the strand, are composed of curved and 
crossed tubular casts, in cases more than an inch in diameter, and 
appear to represent casts of algae (or of something similar) which 
settled in the mud. From this state of irregularity it is but a 
step to nondescript markings the origin of which is probably 
inorganic. 
Owing to the occurrence of most of the grooves on upturned 
blocks and to the fact that the beds underlying the casts have 
not been seen, it is not always possible to determine the original 
direction of the markings. In Sec. 11,.T. 21 N., R. 11 E. it is 
NeoOm Ve in) Sec.)tomd4 25) N.. R. ig E., N: 44°—52° W., which 
directions are down the depositional dip. 
Plant remains have been found in one of the sandstone blocks 
associated with the grooved blocks in Sec. 8, T. 20 N., R. 12 E. 
and they occur in sandstone stratigraphically within a few feet 
of the grooves in Sec. 11, T. 21 N., R. 11 E. Casts of tree trunks 
have been found in abundance in the section roo feet from the 
grooves in the former locality and the very fossiliferous Avant 
limestone is 80 feet from the grooves in the latter locality. 
HYPOTHESES OF ORIGIN 
Various hypotheses may be presented for the origin of the 
grooves: (1) impressions of plant remains, (2) dragging of parts 
of trees or roots, of algae or of pebbles over the strand, (3) action 
of ground ice molding unconsolidated sandy clays, (4) differential 
slipping of the beds before consolidation, (5) tidal action. ‘These 
hypotheses will be examined in order. 
1. Impressions of plant remains.—Trunks of trees or branches 
of algae impressed on the sandy mud could not have made the 
parallel striations such as are shown in Figure 1. They may well, 
however, account for some of the single markings, such as Figure 6. 
Definite worm trails are found on sandstones associated with the 
