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CAPE COD GEOLOGY 



of 100 feet, which appears to be the greatest height reached by any dune in 

 the district. By comparing the present position of the dune ridge with its 

 position as shown on Graham's chart McClintock 1 concluded that the ridge 

 had steadily moved inward from the ocean toward the harbor at a rate of about 

 10 feet a year. "The north wind," he writes, "as a motive power annually 

 carries more than one million tons of sand a distance of half a mile from the 

 northern front to the rear of the ridge." In the same report Mr. Heman S. Cook, 

 a native resident, testified that sand is blown in by the north wind but by no 

 other. The result of this general southerly movement of the dune is to bare 

 the surface that was once covered by the sand on the north side, revealing one 

 or two sets of buried soils containing stumps of trees, and to bury the living 

 forest on the south side. On its east side the ridge has thus partly merged into 

 the outlying dunes known as Mounts Ararat and Gilboa on Graham's chart, 

 though these dunes still retain their general forms and altitudes. Intermediate 

 points, however, have been much altered by the blowing away of the sand, 

 which is driven southeastward by strong northwest dry winds. 



South of the main line of dunes north of Great Pond stands Negro Head, 

 the northeast arm of a horseshoe-shaped dune that is open to the northwest, 

 as shown on Graham's map of 1835. At that time Negro Head had an elevation 

 of 88 feet. This dune has been much altered in form and somewhat reduced in 

 altitude. Farther east, a ridge of dunes that skirts the northern margin of ponds 

 or sloughs stretches toward Pilgrim Lake. This ridge includes Mounts Gilboa 

 and Ararat of Graham's chart, which had elevations of 106 and 100 feet, 

 respectively, in 1835, whereas, according to the survey of 1887, Town Hill, the 

 site of the Pilgrim Monument, was the only dune on the hook having an elevation 

 of 100 feet. 



The dunes between the ponds and Race Run form three well defined belts, 

 which taper out westward. One of these belts borders Race Run, and the Snake 

 Hills of Graham's chart form the oldest one of three. The depressions between 

 these ridges are of the same origin as Race Run, the unfilled space behind succes- 

 sively offset bars growing westward parallel to the shore. 



Between these outer dune ridges and the shore of the harbor the wind, in 

 forming and reforming dunes, has produced a topography that masks the 

 original alignment of the dunes along the earliest bars and beaches. 



There are three of these groups of dunes, which present rather steep fronts 

 to the harbor. One group rises back of Clapp's Pond and extends eastward 



1 McClintock, John N., Report of the Trustees of Public Reservations on the subject of the Province 

 Lands, Feb., 1893, Mass. House . . . No. 339, pp. 16-17, with accompanying map of the Province Lands. 



