. STRATIGRAPHIC CONFORMITY AND UNCONFORMITY 293 
THE COASTAL PLAIN OF EASTERN NORTH AMERICA‘ 
The coastal province includes, as we have seen, the coastal 
plain and the continental platform. Concerning the geologic his- 
tory and structure of the former our knowledge is fairly full and 
accurate and it is becoming more so with every new boring and 
excavation; while our knowledge of the latter is, and apparently 
must remain, largely conjectural or, more accurately, inferential, 
consisting of more or less valid deductions from what is known of 
the coastal plain. Hence it is natural that attention should now 
be concentrated upon the latter, although it is much the smaller 
part of the province. It is, however, the landward part and there- 
fore the part that has been most affected by changes of level and 
consequent migrations of the shore; and it is for this reason, 
especially, much the more promising part as a field for the study 
of unconformity. A brief outline of the geologic history of the 
coastal plain will serve to bring into view the general relations of 
the strata which are the main objective of this paper, relations 
which are believed to hold for coastal plains generally, throughout 
the world and throughout geologic history. | 
During Jurassic time, what is now the Atlantic seaboard of the 
United States was elevated and suffering erosion; and on the com- 
plex geologic structure handed down from Paleozoic and older and 
from Triassic times was developed the so-called Cretaceous pene- 
plain. This peneplained surface of the older formations is the true 
foundation or bed-rock of coastal plain geology—the floor and 
primary datum plane of coastal plain stratigraphy. 
The subsequent history of the seaboard is comprised in an 
oscillatory and possibly isostatic seaward tilting of the Cretaceous 
peneplain, attended landward by erosion, resulting, during periods 
of relative stability, in the partial development of successively 
lower base-levels; and attended seaward by more or less continu- 
ous deposition and the development of the entire coastal plain 
« This paper is one of the fruits of a somewhat elaborate study of coastal plain 
geology made under the auspices of the Board of Water Supply of New York City, 
with special reference to the geologic relations of the ground-water of Long Island. 
This investigation will, in due course, be published in full as a bulletin of the New 
York Geological Survey. 
