STRATIGRAPHIC CONFORMITY AND UNCONFORMITY 295 
varied greatly longitudinally or in the trend of the coast; and 
transversely their differential effect must have been most marked 
because of the normal seaward tilt, increasing downward, of the 
coastal plain formations. The major divisions of these formations 
may be correlated with the major oscillations of the crust; and the 
principal unconformities are, therefore, interformational; while 
relatively local and subordinate unconformities may be described 
as intraformational or, better, as marking off, or giving distinctness 
to, the minor divisions of the geologic record. 
The main point demanding attention now, however, is the 
striking contrast of all these coastal plain unconformities, both 
inter- and intraformational, to the great unconformity of the 
Cretaceous peneplain, forming the floor of the entire coastal plain 
series and recording a hiatus and a stratigraphic break of the 
first magnitude. This basal unconformity of the coastal plain is 
characterized by the profound deformation (plication, faulting, 
etc.) and metamorphism as well as by the extensive erosion of the 
diverse bed-rock formations before the deposition over them of the 
coastal plain series began. In other words, this unconformity is 
the joint product of deformation and erosion, while all the uncon- 
formities, both major and minor, actually within the coastal plain 
series are characterized by erosion alone, and exhibit no sensible 
deformation of the older before the deposition of the newer forma- 
tions. In the one case the beds are discordant, and in the other 
case they are accordant in dip and strike. 
TERMINOLOGY OF UNCONFORMITY 
Grabau,’ recognizing the numerous examples of accordant 
unconformity in the geologic record and the desirability of a dis- 
tinctive name, has proposed for them the designation disconformity, 
reserving unconformity for the discordant type. This use of the 
prefix dis- is clearly unfortunate, since it implies a divergent and 
not a parallel relation of the strata. It is, moreover, desirable 
that we should have a generic term, applicable to all cases of a lack 
of conformity; and for this purpose unconformity has the sanction 
of usage and etymology. Unconformity should not, therefore, be 
tA, W. Grabau, Science (N.S.), XX, 534. 
