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CAPE COD GEOLOGY 



operation for several years. The blue clay at Highland Light has been used 

 locally. A thick section of this clay is exposed along the shore of the bay for 

 more than a mile south of the railway station of North Truro. This and other 

 beds of clay on Cape Cod generally occur in lenses, as they do beneath the light- 

 house at Highland Light, forming the so-called "clay pound," or they appear 

 above sea level as the arches of low folds known as ' 'clay heads." 



Small beds of clay are exposed in the western islands of the Elizabeth group 

 and large beds of blue clay on Block Island, but the most valuable clays in the 

 district are the white, red, and mottled clays and kaolinites of Marthas Vineyard, 

 found on the north side of Gay Head and in the northern part of the main island 

 from the vicinity of Menemsha pond to Makoniky, near Vineyard Haven. Sev- 

 eral attempts have been made to ship this clay for use in making pottery and 

 fire brick. The beds in the western part of the island are highly inclined and much 

 dislocated, being so intricably folded in with beds of gravel and sand that it 

 is desirable to explore the ground thoroughly with the drill before workings 

 are started. There is a small tract at Makoniky in which the white Cretaceous 

 kaolinite is less disturbed, and at that point an extensive plant having kilns 

 for burning several varieties of brick has been operated. The necessity of ship- 

 ping the clay by boat to the mainland is an obstacle to its successful competition 

 with other similar clay for which all-rail transportation is available. 



The beds of Cretaceous white clay at Ball's Point, Clay Head, on Block 

 Island, and of lignitic clay farther south are too small and too much covered by 

 Pleistocene beds to find other than occasional local use. 



The beds of lignite in the Gay Head cliffs contain nodules of marcasite 

 and acicular crystals of selenite, and the bed of greensand at the same place 

 contains phosphatic nodules, but these materials are specimens suitable for 

 display in a case containing natural history objects rather than useful substances; 

 and this remark applies also to the fossil bones and sharks' teeth found at the 

 same locality. 



The bed of Miocene greensand, usually turned reddish brown where it is 

 exposed, has been exploited mainly in the cliffs at Gay Head, east of the light- 

 house. The material might be valuable as a fertilizer of the sandy soil of the 

 island, where it occurs in sufficient quantity to be utilized, but I am not aware 

 that any experiments have been made with it. 



The water supply of Cape Cod is abundant, though most of it is under- 

 ground. The same is true of Nantucket and of the eastern and southeastern part 

 of Marthas Vineyard. In the upland part of Marthas Vineyard and on Gay 



