Haiteras Axis in Triassic and i)i Miocene Time, — Glenn. 377 
resistance to extrusive flows than did the more strongly de- 
formed crust of this northern region. In other words, it would 
seem that this southern-Virginia-Xorth Carolina region as 
compared with the more northern Triassic areas yielded less 
during Triassic time to deformation, or was a region of com- 
parative stability. 
While a close study of the structure of this southern por- 
tion of the Triassic has never been made, yet the facts at hand 
indicate that the magnitude of the faulting here was proliably 
not so great as in the more northern areas. This faulting with 
its accompanying dyking presumably m.arked the close of the 
Triassic and would indicate that at that time, also, this south- 
ern-\'irginia-North Carolina region was a region of compara- 
tive stability. 
McGee speaks of the Potomac thinning in passing from 
\'irginia into North Carolina, being but a few feet thick at 
Weldon and in the vicinity of Wilson being absent, probably 
because of removal through degradation.''' Some distance 
southward of this point, along the line between North and 
South Carolina, the writer has seen it well developed. There 
would seem to be a thinning of the Potomac then acro.s- a 
part of central North Carolina because either of non-deposi- 
tion or of subsequent erosion. 
The upper, marine Cretaceous has a thickness of at least 
five hundred feet in the southern portion of the North Carolina 
coastal plain, as is shown by a boring in it at Wilmington. 
During upper Cretaceous time, then, there must have been 
considerable subsidence in this region, but data are not at 
hand to determine whether it w'as as great as the subsidence 
to the north and to the south or not. 
Here and in the adjacent part of South Carolina the mar- 
ine Cretaceous is often exposed at the surface in stream cut- 
tings, and in the slight depressions in its eroded surface are 
found here and there isolated patches of Eocene or of Miocene 
deposits a few feet in thickness. During the earlier part of 
Eocene time, therefore, th& region must have remained above 
sea-level so long, while the Cretaceous peneplaned surface on 
which the Eocene patches rest was being developed, that when 
it subsided it either received but a thin deposit of Eocene or 
*Amer. Jour. Sci., 3d Ser. vol. 40, p. 20, 1890. 
