2098 WO. CROSBY 
resultant structure would be markedly differént from sphenocon- 
formity; and essentially the same may be said for graben deposits. 
GENERAL CONCLUSIONS 
The Atlantic and Gulf coastal plain of the United States is 
believed to be a normal example of the coastal plains of the globe, 
and to be representative of the conditions under which, chiefly, 
sedimentary rocks have been formed in the past. The contact of 
the coastal plain sediments with the ancient floor or bed-rock sur- 
face on which they were deposited is everywhere the true and 
strongly marked clinunconformity of the Cretaceous peneplain. 
Above this peneplained floor, the coastal plain sediments are 
divided, landward, by repeated parunconformities developed dur- 
ing its progressive, oscillatory subsidence; while seaward they are 
apparently characterized through their entire thickness by the 
uninterrupted sphenoconformity indicative of continuous sedimen- 
tation, increasing in amount seaward or away from the source of 
the sediments owing to the constantly increasing divergence in that 
direction of its limiting planes—the Cretaceous peneplain and the 
surface of the sea. 
When the coastal plain shall have been completed and its sedi- 
ments, through the agency of deformation and metamorphism, 
shall have been added to the rigid crust these original structures 
will still persist. This entire body of post-Triassic sediments will 
be seen to be sharply limited downward by a strongly marked 
clinunconformity. Its original landward margin will be divided, 
as now, into a succession of terranes by an almost indefinite sequence 
of parunconformities, each the record of a complete crustal oscilla- 
tion devoid of deformation; while throughout its more seaward 
portion, now largely embraced in the continental platform, the 
stratigrapher will be baffled by a blending sphenoconformity and 
a general absence of sharply defined stratigraphic boundaries. 
Note.—Since this paper was written, my attention has been called to 
Arnold Heim’s Monograph on “Die Nummuliten- und Flysch-bildungen der 
Schweizeralpen” (Abhandlungen der schweizerischen paleontologischen Gesell- 
schaft, XXXV (1908), 173, in which he makes approximately, but not exactly, 
the same distinction between divergent and parallel uncomformity that is pro- 
