PETER SANDSTONE 
295 
this central area of marked relief would surely have planed away 
the hills of the old land-surface, had they not been mantled 
by sand. To this it can be replied that in Arkansas, where there 
is no visible notable relief in the top of the Canadian or Beek- 
mantown formations, the first deposit laid down was a marine, 
fossiliferous limestone. In Missouri, on a surface of large local 
relief (over 40 feet in 100 yards) the first deposit over a con¬ 
siderable area was a complex of interbedded limestones and sand¬ 
stones. In these cases the waves clearly were not prevented from 
planing away the hills by any protecting mantle of sand, and 
still the hills remain. The objection, therefore, has little weight. 
At the time of the Peter deposition it is believed that the pre¬ 
vailing continental slope was southward. The irregularities of 
depth carried by the hills and valleys would surely exert a pro¬ 
found influence on, currents, and since it is quite impossible to 
map the shoals and possible islands in the Peter sea, it is quite as 
impossible to describe its currents. These were undoubtedly of 
importance in distributing the Peter sands. 
An objection is sometimes advanced that the hills and valleys 
would prevent distribution of sands by the waves. On the other 
hand the same features are cited as barriers to dune-migration. 
Neither interpretation seems to be well founded, since in either 
case the sands would, as they migrated, simply fill each valley 
until it began to spill over the ridge, into the next valley. In 
this way, there could gradually be established on the submarine 
slope a gradient which would ultimately become a graded slope 
for the given depth, size of waves, strength of currents, and sup¬ 
ply of sand. Gradually, from time to time, by warping, shifting 
of shore-lines, or modifications of the rate of supply of sand, this 
gradient would be rendered flatter or steeper. 
It does not seem to be necessary, as so many have supposed in 
the past, that there must be an advancing or retreating shore¬ 
line to enable the sea to spread out an even blanket of sand. 
With a constant source of supply, and a stable land-mass, there 
seems to be without doubt that such a graded slope would be es¬ 
tablished, down which the sand must move so long as the basin 
was not filled up. As the basin becomes shallower and the grad¬ 
ient less, the rate of advance of the sand-mantle would become ex¬ 
ceedingly slow, just as in the final stages of peneplanation. 
Probably the Peter sands were actually laid down in deeper 
