154 SURFACE GEOLOGY. 
observed near the south end of this brick-yard. A mass of uniformly 
blue clay occupies a wedge-shaped space in the midst of gray clay. No 
difference, except that of color, could be seen; and the lines of stratifica- 
tion are plainly continuous through both. 
At the second brick-yard 3 feet of sand overlies 15 feet of clay, which 
rests on a ledge. The upper part of this bed is compact gray clay, in- 
clined to break into small fragments, the sides of which are stained with 
iron-rust; its lower portion is tenacious, and bluish gray in color. 
Near Gonic the stratum is worked at four places, all on the east side 
of the river. Here the surface is 1 to 4 feet of sand. Next follows 10 
to 15 feet of gray clay; this changes abruptly to blue clay, which is sev- 
eral feet thick, and extends below the excavations. 
The brick-yard at Dover landing shows the following deposits, sepa- 
rated by definite lines: Sand at the top, 8 feet; gray clay, 12 feet; blue 
clay, 15 feet. A brick-yard beside the Piscataqua river, half a mile north 
from Dover point, shows 30 feet of clay,—its upper portion gray and its 
lower portion blue. The brick-yards on the south-west side of this point 
expose only the gray clay, which is about 15 feet thick, overlain by 2 or 3 
feet of sand. We find here the features which usually mark the gray 
clay. Near the top it is free from sand, and is hard and compact, not 
showing its stratification, but breaking into small angular pieces, which 
are separated by films of iron-rust. In its lower part it shows lines of 
stratification, and sometimes contains sandy layers. Through the whole 
deposit pebbles up to six inches or one foot in diameter are rarely found. 
A well at one of these yards showed the bottom of this gray clay inter- 
stratified with sand and gravel, beneath which was blue clay. 
The brick-yards along the Boston & Maine Railroad are similar to the 
foregoing. Half-way between the stations of Exeter and East Kingston 
beds of clay are found in kame-like banks, 20 to 30 feet in height, at both 
sides of the railroad. The top of these deposits is a few feet of sand or 
fine gravel, irregularly bedded as if laid down by strong and conflicting 
currents. The clay is nearly level in its stratification, and has a depth of 
about 20 feet. It is principally gray, but changes gradually near the bot- 
tom into blue clay. Another brick-yard of the same kind is found a mile 
farther south. These seem to be isolated deposits, having been formed 
like the kames in hollows of the melting ice-sheet. They lie on the till, 
