The architect of the river builds with sand .

July 19. 

P. M. — Up Assabet. 

The architect of the river builds with sand chiefly, not with mud. Mud is deposited very slowly, only in the stagnant places, but sand is the ordinary building- material. 

It is remarkable how the river, while it may be encroaching on the bank on one side, preserves its ordinary breadth by filling up the other side. 

Generally speaking, up and down this and the other stream, where there is a swift place and the bank worn away on one side, — which, other things being equal, would leave the river wider there, — a bank or island or bar is being built up on the other, since the eddy where, on one side, sand, etc., are deposited is produced by the rapidity of the current, thus : 


— e. g. north side of Egg Rock, at Hemlocks, at Pigeon Rock Bend, at Swift Place Bank, etc., and on main stream at Ash Tree Bend. 

The eddy occasioned by the swiftness deposits sand, etc., close by on one side and a little offshore, leaving finally a low meadow outside where was once the bed of the river.

There are countless places where the one shore is thus advancing and, as it were, dragging the other after it. 

I dug into that sand-bank, once sand-bar, at the narrow and swift place off Hildreth's, five and a half feet deep, this afternoon. It is more than a rod wide and covered with willows and alders, etc. It is built up four or five feet above the summer level. It is uniformly fine sand, more or less darkened with decayed vegetation, probably much of it sawdust, and it has been deposited this depth here by the eddy at high water within a very recent period. 

The same agent is in a great many places steadily advancing such a bar or bank down the stream a rod or more from the old shore. The more recent and lower extremity of this bank or bar is composed of sawdust and shavings, almost entirely so to a depth of two feet. Before it reaches the surface, pads spring up in it; when [it] begins to appear, pontederia shows itself, and bulrushes, and next black willows, button-bushes, etc. The finest black willows on the river grow on these sand-banks. 

They are also much resorted to by the turtles for laying their eggs. I dug up three or four nests of the Emys insculpta and Sternothcerus odoratus while examining the contents of the bank this afternoon. This great pile of dry sand in which the turtles now lay was recently fine particles swept down the swollen river. 

Indeed, I think that the river once ran from opposite Merriam's to Pinxter Swamp and thence along Hosmer's hard land toward the bridge, and all the firm land north of Pinxter Swamp is such a sand-bank which the river has built (leaving its old bed a low meadow behind) while following its encroaching northeast side. 

That extensive hard land which the river annually rises over, and which supports a good growth of maples and swamp white oaks, will probably be found to be all alluvial and free from stones. The land thus made is only of a certain height, say four to six feet above summer level, or oftener four or five feet. At highest water I can still cut off this bend by paddling through the woods in the old bed of the river. 

Islands are formed which are shaped like the curving ridge of a snow-drift. Stagnant rivers are deep and muddy; swift ones shallow and sandy. 

Scirpus subterminalis, river off Hoar's and Cheney's, not long.

H. D. Thoreau, Journal, July 19, 1859

It is remarkable how the river, while it may be encroaching on the bank on one side, preserves its ordinary breadth by filling up the other side. See June 15, 1852 ("Methinks there is a male and female shore to the river, one abrupt, the other flat and meadowy. Have not all streams this contrast more or less, on the one hand eating into the bank, on the other depositing their sediment? "); July 18, 1852 (" Thus by a natural law a river, instead of flowing straight through its meadows, meanders from side to side and fertilizes this side or that. . . The river has its active and its passive side, its right and left breast.")