Davis.] 
372 
[January 18 , 
channels will enclose a faintly marked basin, very shallow, with 
muddy bottom and sides, and exposed to frequent invasion by 
the river that built its barriers. Pontchartrain with a surface of 
twenty by forty miles, is only twenty-seven feet deep ; it lies 
between the Mississippi delta and that formed by the Pearl 
River ; Lake Borgne of later beginning is not yet finished. The 
Holland delta-region of the Rhine and other rivers of Northwest- 
ern Germany contains many lakes and swamps large and small 
of this origin ; the Zuyder Zee being probably a hybrid 
between this species and the Sand Bar Lagoons. Other examples 
may be found on nearly all delta districts, but are often hybrids, 
like the last named. 1 
Some swamps and lakes of the Yirginia and Carolina Coast — 
Drummond in Dismal Swamp, Phelps and Mattamuskeet in the 
Great Swamp between Albemarle and Pamplico Sounds — seem 
to connect this species and the next : they are very shallow, the 
last named and largest being only four to ten feet deep with 
a surface fifteen by seven miles ; and they occur on the highest — 
not in the lowest parts of their swamps, so that some have been 
drained and converted into good farming lands. 2 
C. 12. New Land Basins. The growth of deposits under a 
sea or lake is not such as to produce a perfect plain : there is 
always some irregularity in the accumulation, and although this 
may be slight, it fails to produce a true level by an amount suf- 
ficient to determine the placing of streams and ponds when the 
surface loses its continuous water covering. The manner of its 
conversion into dry land gives means of noting three subspecies. 
First, gentle elevation without dislocation, and of amount just 
enough to cause emergence, brings the former sea bottom within 
range of observation ; in this way the eastern part of Buenos 
Ayres has been added to South America, and its surface is marked 
with numerous shallow pools 3 caught at points of least deposit 
from their very moderate elevation and the extreme flatness of 
1 See maps of deltas of Rhone, Nile, and many other rivers in Credner’s Monograph 
on Deltas, Peterm. Geogr. Mittheil. Erganz’h. 56, 1878. 
2 Kerr, Geol. N. Car. 13. “Dismals” and “Pocosins” are local names for these 
swamps. > 
3 Peterm. Geogr. Mittheil. Erganz’h. 39. 
