96 SURFACE GEOLOGY. 
fifty years built up the largest city in the state. The plains on the west 
side are extensive, both north and south of Piscataquog river, descending 
from 280 to 265 feet above the sea. The upper edge of the alluvium in 
the north-east part of the city is from 260 to 265 feet above the sea. 
Elm street lies upon a terrace intermediate between the high plain and 
that of the depot. Wells upon this street show about 25 feet of common 
sand, in the lower part of which water is obtained by the shallower wells; 
then, 20 feet of quicksand, with no springs, beneath which is a thin layer 
of clay, lying on unmodified drift or till. The deeper wells find their 
springs between the clay and till. 
Piscataquog village also lies mainly upon an intermediate terrace, which 
extends a mile to the south, being occupied by the river road. The low- 
est terrace appears between this and the river; farther south it attains a 
large width, and is crossed by the river road at Bowman’s brook. The 
same terrace is also wide on the east side north of Goff’s Falls. 
About a mile south from the city of Manchester an extensive, ledgy 
hill, isolated in the alluvial area, lies between the Concord and the Man- 
chester & Lawrence railroads. The plain below this barrier to Goft’s Falls 
does not quite reach its normal height, being 210 feet above the sea, or 
100 above the river at the mouth of Cohas brook. In the north-western 
part of Londonderry it is slightly higher, and large quantities of its sand 
have been blown to the south-east 75 feet above it into irregular mounds 
and ridges upon the hillsides. Southward, the high plains are contin- 
uous and wide to Hudson. 
On the west side the plains are wanting most of the way for six miles 
from Bowman’s brook in Bedford to Reed’s Ferry. This side of the val- 
ley appears to have been specially subjected to the erosion of the river, 
which has in many portions removed nearly every trace of modified drift, 
leaving the till or ledge sloping to the present channel. The till is fre- 
quently exposed in the banks or bed of the river between Manchester 
and Nashua, and also sometimes appears on the surface of the extensive 
plains, showing that the modified drift has not so great a depth as in the 
widest portions of this valley northward. Nearly opposite Goff’s Falls, 
and on Sebbins brook at the south line of Bedford, the alluvium expands, 
forming three terraces, the highest in each case being go feet above the 
river. 
