Geology of the Hanover, N. H., Quadrangle.

C. H. HITCHCOCK.

1 625009

The United States Geological Survey has just issued one of their quadrangles upon the scale of one mile to the inch, for the area of 223.5 square miles upon which the village of Hanover, N. H., is situated. About two thirds of the area is in the state of Vermont, including parts of Norwich, Sharon, Pomfret, Hartland, Windsor and West Windsor and the whole of Hartford. As every one knows, the east border of Vermont is the west shore of Connecticut River at low water mark. It will take sixteen quadrangles the size of this one to complete the area of a square degree of latitude and longitude. The Hanover quadrangle is embraced between latitudes 43° 30′ and 43° 45', and the longitude 72° 15′ and 72° 30'. The Strafford quadrangle lying just north of the Hanover area was published in 1896, and the Sunapee quadrangle just touches the Hanover quadrangle at its southeast corner. All three quadrangles have the same scale and their combined area is isolated from all others.

Topographically the Hanover quadrangle is marked by the valley of the Connecticut River running about N. 15° E. S. 15° W., and by the large tributaries, White and Ottaquechee rivers, upon the Vermont side. In Hartland there is a smaller tributary known as Lull's Brook. Upon the east side are three tributaries of about the size of Lull's Brook, viz.: Mascoma River in Lebanon, Blood's and Blowme-down brooks in Plainfield. The exact altitudes of the larger rivers are as follows, as corrected from former statements, in Bulletin No. 274 of the U. S. G. S.:

One and one half miles below Sharon village, Strafford quadrangle,

440

Two miles above Sharon, Strafford quadrangle,

460

The Mascoma River falls from 545 feet at Lebanon to 323 at

Meeting-House Hill, north (Strafford sheet),

1,201

Hill west of New Boston (Strafford sheet),

1,482

Hill one mile east of Gile Mountain (Strafford sheet), 1,700

Vershire, height of land, road from Chelsea (near west line), 1,950

One and one half miles south of north corner,

2,020

Theoretically it is supposed that the original surfaces of the two quadrangles constituted a great plain, with a drainage southward along the course of the Connecticut River, and that this plain has been excavated by the streams flowing through it down to their present levels. The original surface has sometimes been termed a pene plain, and much speculation as to its erosion in the several later periods has been indulged in. If the present elevated points should be imagined to be connected by a sheet or plane the present position of a peneplain might be reconstructed. The easiest method of perceiving this plain in the field is to look at the summits extending