1877.] Surface Geology of the Merrimack Valley. 531 
is built, appear to have been brought partly by each of these 
streams and partly from the northwest along the avenue fol- 
lowed by the Wilton railroad, where no stream now exists. A 
continuous belt of alluvium, upon which this railroad is built, 
extends six miles from the Souhegan River in Amherst to the 
plains near the mouth of Nashua River. Its narrowest place, 
three miles from the city, is a third of a mile wide, while its 
widest portions, in the northwest corner of Nashua and south 
part of Amherst, are one and a half miles wide. These plains 
consist of horizontally stratified sand and gravel, and show a 
gradual descent from northwest to southeast, amounting to sey- 
enty-five feet in the six miles. 
Kames. Remarkable ridges of coarse, water-worn gravel, fre- 
quently interstratified with layers of sand, and sometimes inclos- — 
ing large, angular bowlders, occur in the Merrimack Valley in 
Thornton, Franklin, Boscawen, and Concord; in a series twenty 
miles long, which extends from Loudon along Soucook River to 
its mouth, and thence along the west side of Merrimack River to 
Manchester; in Nashua and Hudson; in another series, which 
has been traced by Rev. George F. Wright, of Andover, extend- 
ing about twenty-five miles, through Methuen, Lawrence, Ando- 
ver, Wilmington, North Reading, and Reading, to Wakefield ; 
along Brandy Brow Brook in Haverhill, and thence continuing 
southward in a series similar to the last; and in Newburyport. 
The plains, terraces, and intervals consist of fine gravel, sand, 
clay, or silt, horizontally stratified; but these ridges are mainly 
composed of very coarse, water-worn gravel, often containing 
Stones two or three feet in diameter. When the gravel is mixed 
with layers of sand, as is frequently the case in the entire section 
of a ridge, these materials are very irregularly bedded, portions 
of them dipping at a high angle, giving the whole a rudely anti- - 
clinal or arched stratification. In many of these ridges, however, 
a section shows no beds of sand, and almost no marks of strat- 
ification ; but there is still evidence that the deposit was formed by 
a current of water. It contains only the smaller bowlders which 
Would be thus separated out from the coarse glacial drift or till; 
these have been more or less rounded by water-wearing, being 
quite different from the glaciated stones of the till, while the sand 
and clay have been mostly swept forward by the strength of the 
Current. Wherever the ordinary fine alluvium has been depos- 
‘ited it overlies or in part covers the gravel ridges, which are 
therefore the oldest of our modified drift deposits. Similar 
