1877.] Surface Geology of the Merrimack Valley. 527 
These dunes occur only on the east side of the valley, consist 
wholly of fine sand, and lie in trains which ascend from the 
highest terrace in a southeast direction along the hill-side. All 
these characteristics indicate that they owe their origin to the 
transportation of sand, by the prevailing northeasterly winds, 
from the plains below, probably at the period when these had 
their greatest extent, prior to their excavation by the river, and, 
we may presume, before the appearance of a forest. They are 
usually made conspicuous at the present time by being blown in 
drifts, which are so constantly changing that they give no foot- 
hold to vegetation; but when they occur at considerable heights 
the lower portion of the series is generally grassed over, making 
the upper drifts appear isolated on the hill-side. The whole 
train of dunes before mentioned is equal by estimate to a mass 
one thousand feet long, fifty feet wide, and two feet deep, thus 
containing one hundred thousand cubic feet or five thousand 
tons, which has been raised by the wind an average height of 
one hundred and fifty feet. 
Another very good illustration of this transporting power of 
the wind is found in Sanbornton, one mile southeast from Hill. 
Here, as also in New Hampton, the ancient dunes have been 
Swept forward anew since the land was cleared. The sand from 
a hollow one hundred and fifty feet long, forty feet wide, and two 
to five feet deep has been carried, in long northwest-southeast 
drifts, two hundred to four hundred feet farther and twenty-five 
to thirty feet higher up the hill. The depth of recent excavation 
is shown by a large stump which has been thus undermined. 
Similar dunes, high above the ordinary modified drift, occur 
along the east side of Connecticut River in New Hampshire and 
Southeast from Ossipee Lake. 
From New Hampton to Bristol the river flows westerly, al- 
Most at right angles with its general direction, descending by a - 
nearly continuous slope eighty-six feet in the four miles, this 
being the most rapid portion of its course south of East Branch. 
Here it is closely bordered by sloping hills, and differs from all 
the rest of this valley in New Hampshire in being well-nigh 
destitute of modified drift. -The high terraces reappear below 
Bristol, and thence to Franklin have a height one hundred and 
to one hundred and seventy-five feet above the river. 
| From Franklin to the Massachusetts line the ancient high 
flood-plain of the Merrimack is everywhere well shown by con- 
Spleuous terraces. Along much of the way these terraces expand 
