MODIFIED DRIFT ALONG MERRIMACK RIVER. 73 



Dunes in Merrimack Valley. 



In the north part of New Hampton, and in many places for thirty miles 

 southward to the north line of Concord, we find numerous dunes or sand- 

 drifts lying at various heights on the east side of the valley, up to 300 

 feet above the highest terraces. Near their beginning, two miles south 

 of Ashland, these dunes appear in large amount, and reach their greatest 

 height. Here the sand-drifts, one to five feet deep, are strewn in a path- 

 way 10 to 20 rods wide, which extends a fourth of a mile along the hill- 

 side, with a north-west to south-east course, rising 300 feet above the 

 ordinary modified drift, or to a height of about 825 feet above the sea. 

 These dunes of the Merrimack valley, like those along Connecticut river, 

 occur only on the east side, consist wholly of fine sand, and lie in trains 

 which ascend from the highest terrace in a south-east direction along 

 the hillside. All these characteristics indicate their origin, through trans- 

 portation by the prevailing north-westerly 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 foothold to vegetation ; but when they occur at considerable heights, 

 we generally find the lower portion of the series grassed over, making 

 the upper drifts appear isolated on the hillside. This is the case at the 

 locality described in New Hampton. The upper part of this series, ex- 

 tending an eighth of a mile, is still in motion, and has been gullied and 

 channelled by the wind often 3 to 6 feet deep over spaces 50 to 100 feet 



Dunes, 



Fig. 18. — Section in Bridgewater and New Hampton. sea. 



Length, \\ miles. 



long, and carried forward, probably some portions 300 feet ahead and 50 

 feet higher, within fifty years. The whole train of sand-drifts at this 

 VOL. III. 10 



