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 i 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 toj:) 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, 



