THE ORIGIN OF CERTAIN PALEOZOIC SEDIMENTS 241 
uncovered for a part of the time each day; in the tropics where the 
water is warm; and in the cold waters north of the polar circles. 
The remarks of Saville Kent concerning the disklike fragments 
of Halimeda mingled with the sands of the great barrier reef are very 
suggestive of the disklike structures here described. The range 
in size of these disks is very much greater than that found in the 
modern Halimeda but it is quite possible that a giant Halimeda-like 
form existed in these early paleozoic seas and gave rise to the struc- 
tures here described. 
One feature of the conglomerate beds yet awaits explanation; 
namely, the peculiar position frequently occupied by the broad 
flat pebbles, either on edge or at any angle to the bedding planes. 
Several explanations of this feature have previously been offered. 
As noted above, Seeley believed these pebbles were formed by 
sponges growing in place. Stose thought that they were formed 
by thin limestone layers breaking into small flat plates or shingle and 
tossed about on a tide-swept flat. When the tide came in, these flat 
fragments were washed together in all positions and held by a soft 
paste which surrounded them. This explanation seemed impossible 
to the author for two reasons: first, it would not account for the 
wide variations in the thickness of the conglomerate beds, which 
varies from a few inches to several feet, each bed being a definite 
unit and separated from those adjacent by parallel bedding planes; 
and secondly, it seemed impossible to conceive of the physical 
conditions which could roll these flat pebbles around until their 
edges and corners were rounded and then leave them indiscrimi- 
nately mixed with a soft matrix, some lying flat, some on edge, and 
others at all possible angles between these two. 
The true explanation of the origin of these conglomerates 
became apparent when a locality was visited along the railroad 
cut of the Lewisburg and Tyrone division, Pennsylvania R. R., 
beside the Logan Branch of Spring Creek, at a point opposite the 
Nittany Furnace in Bellefonte. At this point several hundred 
feet of limestone beds are exposed in a steeply dipping series along 
the railroad cut. The excavation in this cut has exposed the beds 
in vertical section and the arrangement of the broad flat pebbles 
becomes at once apparent. This arrangement is clearly shown in 
