LOWER CRETACEOUS. 91

  
   
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  
  
 
  

Cretaceous (Patuxent formation) :

FEET.

Hard, light-gray, coarse-grained, arkosic micaceous sand........ 6
Band of hard, dark gray, arenaceous, somewhat micaceous, arko-

sic clay, mottled with purple iron stain.......................- 3-5

Hard, gray, coarse, very arkosic micaceous sand, in places becom-
ing coarser and containing many small quartz pebbles as large

ct St ) 2: Sens eae ER EOE ert 6 Toman ets SoReal eh A at, 6-8
Drab to yellowish and red mottled clay, making a dark band along’

the cliff, becoming micaceous and sandy towards base.......... 4-5
Hard, coarse, arkosic sand, somewhat micaceous................ 3
Dark, bluish-gray, argillaceous, very micaceous sand not well ex-

posed, to: water's: edeei soy isostatic ee ae uatier eee 3

The distance by the river from Wilmington to Fayetteville is 115
miles. The mile intervals are indicated by numbers painted on boards
and nailed to trees growing near the banks. The numbering begins at
the former place and proceeds upstream to the latter.

For the first 4 or 5 miles below Fayetteville the river has a nearly
straight course and the exposures are few and unimportant. At about
milepost 110 the river makes a broad bend from its south-southeast
course around to the east, south and southwest, coming back in line
with its former course at about milepost 100.. For a number of miles
along the right bank of the northern limb of this bend and along the
left bank after it turns to the south and southwest, the Patuxent beds
are remarkably well exposed in bluffs ranging from 25 to 50 feet in
height. The materials consist of layers of compact, partially indu-
rated clays and arkosic and micaceous sands, from a few feet to 10 or
12 feet in thickness, making broad light and darker bands along the
faces of the bluffs, the sections being similar in all essential respects
to those farther up the river previously described. The beds are
almost horizontal, it being possible to trace the bands along the bluffs
for a number of miles without detecting any appreciable dip.

_ One of the striking features to be observed along the face of these

bluffs is the effect produced by the water of the brooks and springs

which enter the river through little overhanging valleys, on the sands

; and clays of the Patuxent formation over which ‘it descends. It

seems that these materials, kept constantly moistened, are rendered

more resistant to the eroding effects of the high waters of the main

stream than the adjacent materials of the same layers which are sub-

jected to repeated wetting and drying so that the latter are cut away

ae more rapidly, leaving the former standing out as rounded projections

4 or 5 feet in thickness at right angles to the face of the bluff, and
from 10 to 25 feet or more in height. See Plate II, B.

The upper 10 to 15 feet in all these bluffs is made up of Pleistocene