PARTLY DISSECTED PLAINS IN JO DAVIESS COUNTY 737 
old beaches, etc., in places where protected from later erosion. 
(i) Marine fossils might be found on the surface of the plain. 
Of these features the plain under discussion has some and 
lacks others. (a) It has no hills above it; (0) the underlying for- 
mation has a sufficiently uniform thickness to give the idea of an 
original plain; (c) the relief of the surface is sufficient but not too 
great; (d) the plain follows the structure fairly closely; the slope 
of the flat may be either that of the old sea bottom, or the result 
of slight subsequent tilting; (/) and (k) the materials of the sur- 
face afford no evidence, because there is a complete lack either 
of river detritus or of the shells of terrestrial or marine animals; 
(g) even if old shorelines were preserved at the edge of the ancient 
sea bottom, they would be found only at the margin of the plain, 
and this is outside the region under discussion. But no such shore 
features have been reported, and in all probability none exists. 
Even if the plain had had such a history as is here outlined, the 
factors mentioned in (/), (g), and (#) would not be expected to have 
persisted through such a lapse of time as the hypothesis presup- 
poses. 
4. There remains one other hypothesis to be analyzed and 
tested. If this plain is the result of marine erosion, it would have 
most of the characters of a peneplain due to stream erosion; that is, 
(a) it might have erosion remnants on its surface; (b) it might lie 
parallel with the strata in a general way, but it would be surprising 
if the two were exactly parallel; (c) it would slope in one general 
direction, in this case the slope being the oceanward slope of the old 
sea bottom; (d) some of the plain should be covered with marine 
sediments—debris deposited on the surface after its erosion, but 
before the recession of the sea. This plain would differ from a true 
peneplain in having little or no relief before dissection, and in 
having correspondingly little variation in thickness of the under- 
lying formation within short distances. In addition, a plain so 
made must have been bounded originally by a shoreline of some 
sort, and this might or might not have been preserved, if the flat 
was preserved. Also, as the sea cut its way over the rock surface, 
and the flat off shore became wider and wider, the places eroded 
would gradually become sites of deposition, and this débris might 
