398 THOMAS C. CHAMBERLIN 
sediments, however, usually carry evidences of actual sinking, but 
such sinking must be determined on its own specific grounds. 
17. Great sea-transgressions of the land do not necessarily 
involve great continental depressions; they are more or less due 
to general denudation, to shore cutting, and to sea-rise caused by 
sediment from the land.* 
18. Effective base-leveling implies an absence of crustal move- 
ment while it is in progress.?_ It thus bears on the promptness and 
completeness of isostatic readjustments. 
PERIODICITY OF DIASTROPHISM 
19. Effective base-leveling is evidence that the earth-body is 
strong enough to stand the strain of ordinary loading and unloading 
for a long period without essential yielding; it thus implies that 
isostatic adjustments are periodic rather than continuous, and 
that diastrophism, in so far as it is assignable to such loading and 
unloading, is similarly periodic. 
20. The stages occupied in base-leveling and sea-transgression 
were probably much longer than the intervening stages of active 
deformation. 
21. The mechanism of isostasy implies that great basins once 
formed tend to remain basins permanently, and that great pro- 
tuberances tend to remain protuberances except as worn down. 
Isostasy is not hospitable to great inversions of sea and land. To 
this there may be regional exceptions where great erosion is closely 
paralleled by great deposition. 
22. Since the present isostatic status follows a period of great 
diastrophic readjustment, it is an open question whether the present 
degree of compensation is essentially a consequence of that dias- 
 trophism, or is a normal state approximately maintained at all 
times. 
“The Lateral Stresses within the Continental Protuberances and Their Rela- 
tions to Continental Creep and Sea-Transgression,”’ Article III, Jour. Geol., Vol. XXI 
(1913), p. 585; ‘‘Rejuvenation of the Continents,” Article IV, Jour. Geol., Vol. XXI 
(1913), Pp. 673-75. 
2 “The Rejuvenation of the Continents,” Article IV, Jour. Geol., Vol. XXI (1913) . 
pp. 676-81. 
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