FOURNAL OF GEOLOGY 
MAY TONE, 1012 
DYNAMIC RELATIONS AND TERMINOLOGY OF 
STRATIGRAPHIC CONFORMITY AND 
UNCONFORMITY* 
W. O. CROSBY 
Massachusetts Institute of Technology, Boston 
GENERAL DEFINITIONS 
Next in dynamic and structural importance to the stratification 
of sedimentary rocks are the relations of the strata designated by 
the terms conformity and unconformity. Most briefly defined, 
and with emphasis laid, as it should be, upon the dynamic aspect 
of the phenomena, conformity means that the process of deposition 
was not, and unconformity that it was, interrupted by erosion. 
In other words, conformity implies that deposition was essen- 
tially continuous, that no true hiatus and consequently no period 
of erosion (the antithesis of deposition) intervened during the depo- 
sition of the series of which this structure is predicated. This 
definition, it will be noted, tacitly assumes that deposition does 
not fail absolutely from mere lack of material, where other condi- 
tions are favorable, although over extensive areas, including espe- 
cially the abyssal depths of the ocean, it may be almost infinitely 
‘In the preparation of this paper the author has had the advantage of discussing 
the subject with those two accomplished stratigraphers, Dr. A. W. Grabau and Dr. 
H. W. Shimer; and their helpful criticism and suggestions are gratefully acknowledged. 
Vol. XX, No. 4 289 
