yO SIDNEY POWERS 
Figure 5, the reverse is the case, and there are no depressions in 
the cast. 
Parallelism is the striking characteristic of the markings: they 
are as straight and as parallel as if ruled with a straight-edge. 
Yet frequently the grooves end abruptly, but smoothly as seen in 
Figure 3, or the ridges and grooves in the cast may disappear one 
by one in a deep, curved, and narrow groove whose beginning is 
Fic. 3.—Irregular markings in another block of sandstone at the same locality 
as Figures 1 and 2. Suspended fronds of seaweed waving back and forth could produce 
these sinuous, intersecting fine grooves and ridges. 
one of the grooves, but whose depth (a sharp ridge in the original) 
is fully zinch. Itisasort of festoon, an arrangement very common 
in pahoehoe lava where the rumples in the lava are suddenly 
swept beneath the surface in a smooth curve. Sometimes some 
of the markings end in a rude curve or are curved along their 
length, the original direction being resumed beyond the curve 
(Fig. 2), while the other markings on the same slab are perfectly 
straight. Associated with some of the grooves are irregular small 
depressions and less abundant elevations in the cast (Fig. 2, 
