236 THOMAS C. BROWN 
This series of strata, ranging from the Upper Cambrian well 
into the Ordovician, represents a peculiar combination of odlites, 
rounded sand grains, and unusual conglomerate-like beds which 
requires more than ordinary conditions of sedimentation to explain. 
After detailed study’both in the field and in the laboratory, it seems 
to the author that these structures can be best explained individu- 
ally, and as a combination, by the following series of events. 
Toward the close of Cambrian time an epicontinental sea covered 
this region. The adjacent land area was in a state of peneplana- 
tion, thus furnishing very little clastic sediment but probably 
still contributing considerable quantities of calcium carbonate in 
solution. This lime carbonate was removed from the sea water 
and deposited as limestone by the activities of marine organisms. 
Marine animals, trilobites, brachiopods, and probably many other 
less highly organized types like the sponges aided in this work, 
but the greater part of the separation and secretion of the lime was 
brought about by marine algae which gave rise to the odlites and 
peculiar pebble-like structures. Then the region was somewhat 
elevated and sand-dune conditions prevailed. These marine lime- 
stones were covered over by a thick blanket of wind-blown sand. 
‘This material was worked over by the wind so long and so thor- 
oughly that even the minute grains were rounded into almost 
perfect spheres. This sand resembles, but is even more rounded 
than, the beach and dune sand along the Florida coast today, which 
has gradually been carried southward by the wind and water and 
rounded during its journey. The region was not very far above 
sea-level and at least twice during the accumulation of these sands 
it was submerged and thin beds of limestone similar to those of 
the preceding period were formed. After this complete series 
of sandstones and limestones had accumulated, the whole region was 
finally submerged and the continuous marine sedimentation of 
early Beekmantown time was inaugurated. However, marine 
algae were still the important agents in producing the limestone, 
because, as already noted, odélitic limestone and siliceous odlite 
occur at numerous horizons and a large percentage of the lower 
beds is composed of the peculiar pebble-like conglomerate secreted 
by the algae. 
