139 Parker Mountain

SURFICIAL GEOLOGIC MAP OF THE ALTON QUADRANGLE, STRAFFORD AND BELKNAP COUNTIES, NEW HAMPSHIRE BY RICHARD GOLDSMITH OPEN-FILE MAP PUBLISHED 1995 REVISED DIGITAL MAP PUBLISHED 2006 Geology mapped 1994 DESCRIPTION OF MAP UNITS A variably thin layer of windblown fine-to medium-grained sand and silt less than 3 ft. (1 m) thick is present over much of the surface of the map area but is not shown. The lower part of this layer is generally mixed with underlying surficial deposits. Qal Alluvium (Holocene)—Sand, silt, and minor gravel in flood plains along present-day rivers and streams. As much as 20 ft. (8 m) thick and generally underlain by adjacent deposits. Extent of alluvium indicates most areas flooded in the past which may be subject to future flooding Qw Swamp deposits and wetlands (Holocene)—Muck, peat, silt, and sand underlying poorly drained areas. Generally 5 to 10 ft (1.5-3 m) thick but may be as much as 30 ft (9.1 m) thick. Much of the swamp in the State Merrymeeting Wildlife management Area is probably underlain by lake-bottom deposits of Glacial Lake New Durham Qst Stream terrace deposits (Holocene and Pleistocene)—Sand, pebbly sand, gravel, and minor silt on terraces cut into former glaciofluvial and glaciomarine deposits and till. From 5 to 15 feet thick. Formed along the Merrymeeting River near Alton and Alton Bay as the drainage reversed from south-flowing to north-flowing when a lower, northern outlet for glacial lake New Durham and glacial lake Winnipesaukee became ice free Qac Alluvial-Colluvial deposit—Late-glacial, poorly sorted gravel and sand deposited as a dam in upper Coffin Creek drainage STRATIFIED GLACIAL SAND AND GRAVEL (Pleistocene)—Sand, silt, and pebble to boulder gravel, well-sorted to poorly sorted and stratified, as much as 130 feet thick. Deposited by glacial meltwater streams from the retreating ice sheet. Some deposits are deltas or lake bottom deposits of glacial lake New Durham. Other deposits are deltas or fans built by streams into temporarily ponded areas. The deposits in the quadrangle represent successive northward retreating positions of the ice margin. The successive deposits in each drainage basin are numbered consecutively in order of deposition where the order can be determined. The original form of some of the deposits is not well known partly because of reworking by later erosion, but mostly because of removal of material for commercial purposes LACUSTRINE DEPOSITS Qgln Qglns Deposits of glacial Lake New Durham—Sand, silt, and minor pebble gravel and clay deposited in glacial Lake New Durham, an early stage of glacial Lake Winnipesaukee. The lakes was formed behind bedrock thresholds at about 515 feet a mile south of New Durham corner at Route 11, and at about the same elevation along the Ela River about 3,000 feet to the north-northeast. The lake drained over these thresholds down the Ela River until the ice was well north of the quadrangle. Qgln—lake bottom silt, sand, clay, and organic matter in poorly drained areas. Qglns—sand and minor pebble gravel and silt forming extensive deltas or fans or small near-shore deposits. Locally as much as 130 feet thick Qgls Deposit at Marsh Pond—Sand and pebbly sand deposited in glacial Marsh Pond Qglm Deposit at Merrymeeting Lake—Interlayered pebble-cobble gravel and sand, minor boulder gravel. As much as 80 feet thick. Deltaic deposit into ice-blocked glacial Merrymeeting Lake. Toe of deposits reworked by wave action FLUVIAL DEPOSITS Qcg2 Qgc1 Deposits along Coffin Brook—Qgc1 is a very bouldery ice contact deposit as much as 40 feet thick consisting largely of pebble to cobble gravel with little sand. Qgc2 is an ice-channel filling passing into a small deltaic deposit as much as 15 feet thick Qgm7 Qgm6 Qgm5 Qgm4 Qgm3 Qgm2 Qgm1 Deposits along the Merrymeeting River—Successive deposits of fluvial and deltaic sand and gravel in glacial Lake New Durham as it expanded during ice retreat. The constriction at Alton Bay is occupied in part by a distinct esker formed by a stream that appears to have fed the deposit at Alton (Qgm5). Construction of the now abandoned railroad to Alton Bay has altered the original shape of the deposits northwest of Alton. Thickness of the deposits varies as indicated by the well data Qge2 Qge1 Deposits into glacial Lake New Durham and the Ela River drainage. Qge1 consists largely of cobble-boulder gravel graded to the spillway at about 519 feet on Route 11. Cobble gravel and sand are exposed in the pit at the north end of the deposit. Qge2 is a less coherent deposit laid down amidst residual stagnant ice blocks. This deposit was graded to the northern spillway for the lake at about 515 feet which had now become exposed Qgcp Deposit near Club Pond—Boulder and cobble gravel deposited by meltwater from ice north of the gap. As much as 25 feet thick Qgu Uncorrelated deposits—Isolated deposits of sand and gravel not clearly fitting the pattern of systematic retreat. The long esker or ice crevasse filling near lower Coffin Brook, the small deltaic deposit south of the long esker, and cobble and boulder gravel deposits forming a bench east of Rte 28, 3000 feet north of Stockbridge are about the same age and are older than the deposits along upper Coffin Brook Qgc1 and Qgc2. Deposits adjacent in the area near Stockbridge Corner are largely sand interpreted to be ponded deposits in glacial Lake New Durham Qt Qtt TILL—Non-sorted to poorly sorted mixture that ranges from clay-size particles to large boulders but is dominantly silt to pebble sizes. Matrix ranges from loose and sandy to compact and silty. The till is predominantly sandy in this quadrangle and has been excavated for use locally. Deposited directly by the ice sheet with little or now modification by meltwater. In some places mantles bedrock thinly (to about 10 feet) and discontinuously. Includes drumlins which are streamlined hills of till as much as 80 feet thick and shaped by moving ice. At Prospect Mountain and Ragged Mountain thick till has accumulated on the lee side of these essentially bedrock features af Artificial fill—Earth-fill material that was derived from surficial deposits and/or bedrock in made land. Many small bodies not shown on the map Bedrock exposures—Ruled pattern indicates areas of abundant exposures and areas where surficial cover is thin (generally less than 10 ft [3 m] thick) Contact Approximate retreatal position of the stagnant-ice margin during deposition of designated morphosequence Generalized maximum extent of glacial Lake New Durham Long axis of drumlin—Generally parallel to inferred direction of the ice movement. Not shown on drumlins that are irregular or nearly circular in shape because of possibility of partial control of the shape by subjacent bedrock or subsequent erosion Glacial grooves and striations—Observation at tip of arrow. Number is degrees east of south Meltwater spillway—Controlled deposition of meltwater deposits. Underlain chiefly by bedrock. Letter symbol indicates map unit controlled by spillway Meltwater channel—Erosional features developed mostly in till. In places, acted as the debris-laden melt water feeder for nearby morphosequences Pit in surficial materials—Extent of large pit shown by hachures. Letter symbols indicate predominant texture of exposed materials: s, sand; p, pebble; c, cobble; b, boulder, in decreasing order of abundance: g, gravel; for example, pcg means pebble-cobble gravel, that contains interlayer of sand Abandoned gravel or sand pit Dip of delta foreset beds MATERIALS OBSERVATIONS Texture of stratified deposits—Indicated to depth of at least 5 ft (1.5 m). Gravel Mixed sand and gravel Sand with minor silt .

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