54 The American Geologist. Janey ae 
The present topography of the high plains is strikingly flat, but 
there are saucer-like depressions which are accounted for by localized 
percolation of rain water, at once compacting and dissolving the loose 
Tertiary deposit. Some linear depressions with gentle slopes, well! 
sodded and without a central ditch are also believed to be due more 
to settling and creep than to surface erosion. The large irregular basins 
are of an entirely different type and belong to the areas where the 
Tertiary is underlaid by the Red Beds which abound in salt and gypsum. 
Peds ot the former especially have been dissolved out and have allowed 
the formations above to settle, producing basins, sometimes many miles 
in exrent. Large areas in southwestern Kansas having a tumultuous 
topography, not reconcilable with erosion by water or by wind, are 
explained in this way. 
The chief interest topographically centers about the very existence of 
the high plains. The run-off of this sub-humid strip has been unable 
to make a beginning toward dissecting the surface, while the more 
humid area on the east and the more arid strip to the west are being 
rapidly dissected and degraded. The explanation given relates this 
phenomenon to vegetation. The sub-humid region is the country of 
short grass and thick sod, the most effective protector against the be- 
ginnings of erosion. The slightly less rainfall on the west favors bunch 
grass, which offers little resistance to rill marking and gullying. The 
more lumid climate on the east can produce nothing better than the 
short sod and its more rank vegetation is inferior as a protector against 
dissection, while its greater run-off favors erosion. It is pointed out, 
however, that it is only against the beginnings of erosion that this pro- 
tection is adequate and that the eastern limit of the high plains is sharp- 
ly marked by a definite escarpment, east of which, minute dissection 
and rapid degradation are in progress. Attention is called to the pre- 
carious hold on existence, which these plains have. A heavy rain fol- 
lowing a long drought will find the sod less resistant and may make a 
beginning of gullying which will rapidly destroy the plain surface for 
a considerable area. The relation of this process to “bad lands” is sug- 
gested. 
Many of ike gravel strips are cemented by carbonate of lime, form- 
ing “mortar beds.” The behavior of this salt in comparison with 
others is examined with care. It is shown that its retention in solu- 
tion is difficult in the presence of other salts. It is inferred that the 
deposition of the lime carbonate occurred at the level of ground water, 
and, though the exact reason is obscure, it is suggested that at this 
level the descending rain water in which it was held, came into con- 
tact with the ground water charged with other salts and was thereby 
rendered unable to retain its own. Mortar beds at various levels would 
then indicate fluctuations in the level of ground water, which are to be 
correlated with fluctuations of climate. That they are “cemented on 
levels” and not beds of original structure, is evident from the way 
in which they often follow a level across the various materials and 
irregular structure of the deposits. 
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