DIASTROPHISM AND THE FORMATIVE 

 PROCESSES. VIII 



THE QUANTITATIVE ELEMENT IN CIRCUM-CONTINENTAL 



GROWTH 



T. C. CHAMBERLIN 



University of Chicago 



In a previous article of this series (VI, p. 271) we endeavored 

 to show that the depth of the ocean does not, in itself, set limits to 

 the thickness of the strata laid down in it — when these are meas- 

 ured in the usual way — ^though it does determine the amount of 

 material required to build the continental terraces oceanward to 

 given distances and thus indirectly affects the thickness of strata 

 actually attained b}^ a given amount of material. As a quantita- 

 tive factor, then, ocean depth has its importance in determining the 

 amount of peripheral growth that may arise from a given amount 

 of sediment; or, if the peripheral growth be given, the amount of 

 sediment required to accomplish it and, by interpretation, the time. 

 The unit of such quantitative measurement is found in terms of 

 radial extension rather than stratigraphic thickness. This distinc- 

 tion of terms and methods arises from the fact that the ocean depth 

 affects the area of each stratum because of its inclined attitude. 

 The quantity of sediment in the circum-continental terraces is 

 one of the elements by which the denudation of tributary land 

 is measured; or, the rate of denudation being roughly known or 

 assumed, the amount of sediment in the terraces is a measure of 

 the time occupied in the formation of the terraces. It thus 

 becomes not only an index of the antiquity of the terraces but 

 gives some incidental testimony as to their history. 



In such rough approximations as alone are possible in studies 

 of secular denudation and accumulation, we may assume that the 

 surface movements of the ocean waters were eft'ective in the same 

 way and to the same extent in all ages, though this assumption was 



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