FOREST COVER IN PROTECTING RESERVOIRS 19 
abandoned. Few of these abandoned lands restock to trees, although 
coarse grasses, chiefly broom grasses (Andropogon) usually soon 
clothe them. The area of such abandoned farm lands in the Lake 
States is estimated to be not less than 5,000,000 acres. In addition, 
there are estimated to be more than 31,500,000 acres of burned or 
cut over and subsequently burned or devastated forest land in this 
region, largely destitute of tree growth but often with fair ground 
cover of grasses and small shrubs. Even in the most rugged regions 
there is a minimum of erosion on these sites because of the sandy 
or gravelly soils. Except locally, as in the protection of stream 
banks or when the soils are clayey, forest cover exercises a low pro- 
tective function in most portions of the Lake States region. 
In the New England States, however, the demarcation between 
absolute forest lands and those lands most suitable for farming is 
usually sharply drawn. For this reason further encroachment upon 
the forest lands for farms will not be extensive; and, if the forest 
conditions are not destroyed by injudicious lumbering, the present 
conditions of stream flow can probably be maintained. 
RIVERS OF THE MIDDLE ATLANTIC COAST REGION 
The most important streams of the Middle Atlantic coast group 
are the Potomac, the Delaware, the Susquehanna, the Rappahannock, 
and the James Rivers. There should be included with this system 
the Allegheny and Monongahela and certain other head streams of 
the Ohio which lie within this general region and exhibit similar 
characteristics of flow. 
These streams rise in the Allegheny Mountains, where for the 
most part their headwaters drain narrow agricultural valleys inclosed 
by forested but thin-soiled though permeable shale and sandstone 
ridges. The lower portions of their basins are largely cleared and 
have rather heavy soils and frequently poor humus conditions, both 
in the forests and in the agricultural lands. The forest humus, de- 
rived chiefly from oak, chestnut, and pine, is naturally scant, except 
at high altitudes, and has been further reduced over large areas. 
Burning resulting in insolation of the soil and the compacting effects 
of heavy rains have resulted in light erosion. 
Stream flow is maintained by a rainfall of from 40 to 50 inches, a 
feature of which is a heavy, irregular midsummer precipitation, 
compared with 30 or 40 inches of precipitation on the basins farther 
north. The considerable winter snowfall is usually removed by 
warm spring rains, causing floods, which corrade the banks of 
streams and also erode the agricultural lands. (PL 13.) In addi- 
tion there are frequent summer and fall floods, all accompanied by a 
large silt burden in the streams. The floods damage canals and 
riparian property, and the silt is deposited in the estuary channels, 
where constant dredging is required to maintain depth. 
The silt which is annually discharged by the Susquehanna River 
at Danville, above which point the basin of the river has an area 
of 9,530 square miles, amounts to 240,150 tons. On the James River 
it_has been estimated 17 that, in a flood with a 10-foot crest, from 
275,000 to 300,000 cubic yards of solid matter are moved during 
"Hains, P. C. improvement of the .tames river, Virginia. [U. S.] Sec. War Ann. 
Rpt. 2 (pt. 2, app. J) : 947. 1885. (Rpt. Chief Engin., U. S. Army.) 
