E. D. Chester—Gravels of Southern Delaware. 39 
the estuary waters. Beheath this lowest terrace and that ter- 
race some 200 feet higher up and several miles to the north, 
are traced a number of indistinct intermediate terrace lines. 
One of these, rising some sixty feet above the river, can be 
followed from Wilmington for twenty miles or more to the 
south, keeping for the greater portion of its length the course 
of the Delaware railroad. From the lowest river terrace of red 
gravel, the same deposit is seen to dip beneath a uniform bed 
of black clay, and is always struck in the digging of deep 
drainage trenches along the shore. A deposition of the same 
bog clay is now going on by means of flood-tide, whenever the 
land is unprotected by earth'dikes. It is this impervious layer 
which forms the basis of all the undrained marsh land of the 
river and bay shore. 
PHENOMENA OF THE SOUTHERN AREA. 
General considerations. — Beginning with the latitude of 
Appoquinimink Creek, which marks the southern boundary of 
New Castle County, Del., and extending to the lowermost 
limits of the peninsula, we have an area comprising over four- 
fifths of the entire peninsula. Yet so much of what is observed 
within the larger territory being but a repetition of what occurs 
to the north, the subject of the gravels, in the way it is treated, 
18 about equally divided. Generally speaking, we may say 
that from the northern limit above indicated to about the lati- 
tude of Dover, the region is covered by both members of the 
Delaware gravels, with their usual thickness well maintained 
throughout. They are very morainic in their characters, 
nsing into elevations sometimes reaching fifty feet, with corre- 
sponding depressions. Over the surface everywhere are scat- 
tered an abundance of bowlders, Jarge and small, the upper 
brick clay becoming a stratum of coarse gravel or bowlder clay. 
3 we pass to the south of Dover, however,: appearances 
change, the country becomes gradually less undulating, and 
the gravels less coarse, the change being indeed so gradual as 
He imperceptible. At a distance as far south as Murderkill 
taining smaller rounded pebbles of glassy or jaspery quartz 
pr quartzite, together with subangular fragments of chert 
the surface of the sandy loam, quartzitic bowlders are found, | 
