374 M. L. FULLER — GEOLOGY OF FISHERS ISLAND 



rials and are commonly recognized by drillers, it seems probable tbat the 

 materials are all Pleistocene. 



Resting on the Cretaceous in western Long island, and coming between 

 it and the Jameco gravels with the general relations shown in figure 5, is 

 a series of old gravels of somewhat distinctive characteristics. 



These gravels, which are the oldest Pleistocene beds yet recognized in 

 the region, consist of moderately fine rounded fragments of quartz, with 

 a slight admixture of deeply weathered granite pebbles, having origi- 

 nally a thickness of some 500 feet. They rest unconformably on the 

 Cretaceous and are overlain unconformably by the more granitic beds 

 designated as the Jameco gravels and described on a subsequent page. 

 To the lower and older gravels the term Mannetto * from Mannetto or 

 High hill south of Huntington, Long island, where the beds are best 

 exposed, is applied. 



Figure 5. — General Relations of Cretaceous Beds and the Mannetto and Jameco Gravels. 

 The area shown is the region of the West or Mannetto hills on western Long island, a, Wis- 

 consin and other post-Gardiner sands ; b, Gardiner clay ; c, Jameco gravel ; d, Mannetto gravel ; 

 c, Cretaceous. 



The Mannetto beds are easily recognized by their quartzose character 

 and by weathered granitic pebbles, which can usually be crushed by the 

 fingers or by a slight blow of the hammer. They were deposited during 

 a period of depression when the land in western Long island stood about 

 300 feet lower than at present, the materials being derived from the wash 

 from an ice-sheet which obtained much of its material from the Creta- 

 ceous deposits over which its margin advanced. The deposition fol- 

 lowed a long period of erosion in late Tertiary times, during which all 

 Tertiary and much of the Cretaceous materials were removed. 



The Mannetto beds have not been seen anywhere east of Mannetto 

 hills, but on Fishers island, as has already been pointed out, the inter- 

 val between the dark glacial clay (Gardiner) and the basal blue clay 

 (Cretaceous) is considerably greater than is required for the Jameco 

 gravels ; hence it is not improbable that a considerable thickness of Man- 

 netto beds may be present beneath the island and having the relations 

 shown in figure 4. 



The term " Jameco gravels," which is named from the village of 



* Proposed in manuscript discussion of the geology of the underground waters of Long island by 

 A. C. Veatch. 



