206 W. O. CROSBY 
restricted to a particular type of stratigraphic break, even though 
that one be the most important. 
My first thought was to propose for the two types of uncon- 
formity—the parallel and divergent—the prefixes para- and dis-, 
respectively, thus matching the distinction in physics of paramag- 
netism and diamagnetism. But the prior use of dis- in the con- 
trary sense has seemed to preclude, or at least to render undesirable, 
its use in this new, though etymologically more correct, sense. I 
therefore propose, instead, the prefixes para- and clino-. The terms 
may be written in full, and with a hyphen to aid pronunciation, 
thus, para-unconformity and clino-unconformity; or they may be 
abbreviated to parunconformity and clinunconformity. 
Although these terms are, and, for the sake of convenience in 
designating and describing the phenomena, ought to be, structural, 
it is important, nevertheless, to recognize that the real, the funda- 
mental, distinction, is dynamic; and of course the student should 
not be misled by the fact that a clinunconformity may locally show 
a parallel relation of the strata. The full significance of the dis- 
tinction for which these terms stand is realized only in the broad 
view. We then see that parunconformities must be relatively fre- 
quent and local, recording the minor vertical oscillations of coastal 
plains undergoing progressive and, possibly, isostatic settling; 
while clinunconformities are few and widespread, recording the 
great crustal revolutions accompanied by profound readjustment 
and interchange of land and sea. 
CONFORMITY IN THE COASTAL PROVINCE 
Deposition within the coastal province is limited by two planes 
diverging seaward: (1) the level surface of the sea, the elevation of 
which is constantly shifting, with a general tendency to rise rela- 
tively to the land; (2) the sloping bed-rock surface, the buried 
Cretaceous peneplain. It is a significant fact that if the Cretaceous 
peneplain be projected seaward under the continental platform 
with its proved gradient beneath the coastal plain, it will be found 
at the foot of the continental slope approximately continuous with 
the floor of the abyssalocean. We cannot doubt, therefore, in view 
of the shallow soundings of the continental platform, that the sedi- 
