From the factory dam to the powder-mills.

July 21. 

P. M. — To Assabet, above factory. 

July 21, 2019

For about one third the way from the factory dam to the powder-mills the river is broad and deep, in short a mill-pond. 

Harrington has what he calls his Elm Hole, where he thinks he finds the old bed of the river some ten rods from the present. The river in many places evidently once washed the base of hills, from which it is now separated by fifty rods of meadow. 

The pontederia on the Assabet is a very fresh and clear blue to-day, and in its early prime, — very handsome to see. 

The nesaea grows commonly along the river near the powder-mills, one very dense bed of it at the mouth of the powder-mill canal. The canal is still cluttered with the wreck of the mills that have been blown up in times past, — timber, boards, etc., etc., — and the steep hill is bestrewn with the fragments of the mills, which fell on it more than half a dozen years ago (many of them), visible half a mile off. 

As you draw near the powder-mills, you see the hill behind bestrewn with the fragments of mills which have been blown up in past years, — the fragments of the millers having been removed, — and the canal is cluttered with the larger ruins. 

The very river makes greater haste past the dry-house, as it were for fear of accidents.

H. D. Thoreau, Journal, July 21, 1859

Harrington has what he calls his Elm Hole.See July 20, 1859 ("Hosmer says that when he digs down in his millet- field, twenty rods or more from the river, in his interval, at three or four feet depth he comes to coarse stones which look like an old bed of the river. ")

The pontederia on the Assabet is a very fresh and clear blue to-day, and in its early prime. See  July 18, 1852 ("The pontederias are now in their prime . . .They are very freshly blue. In the sun, when you are looking west, they are of a violaceous blue."); July 18, 1853 ("The fields of pontederia are in some places four or five rods wide and almost endless")

The steep hill is bestrewn with the fragments of the mills, which fell on it more than half a dozen years ago . See January 7, 1853 ("Timber six inches square and eighteen feet long was thrown over a hill eighty feet high.")

Powder-mills. Nathan Pratt purchased a  mill pond dam on the Assabet River and converted the former sawmill to a powder mill in 1835. The first explosion, in the first year the mills were operating, killed four men in 1836. The last three explosions in 1940 ended gunpowder production, and the dam at the original mill pond site is now being used to generate hydroelectricity for municipal Concord. The body of water created by the dam goes by the name Ripple Pond, and is located in Acton and Maynard.~ Wikipedea