the Jerseyan, the Illinoian, and the Wisconsin. The till of Jerseyan age is very deeply weath- 

 ered and only scattered remnants of it are left preserved on divides and on the crests of low 

 hills much as are the remnants of the Mannetto. The Illinoian till is also deeply weathered 

 though less so than the older Jerseyan. It also has been greatly eroded and only small remnants 

 of the formation can now be identified. Beds of sand and gravel, the Bridgeton and Pen- 

 sauken formations are in a sense associated with each of these tills but as they contain the 

 remains of plants which grew in a warm climate they are regarded as interglacial rather 

 than glacial deposits. These two formations are very similar to one another and both closely 

 resemble the Mannetto in composition, degree of weathering, and in the physiographic position 

 of their remnants. The Mannetto then may be related to either the Jerseyan or the so-called 

 Illinoian glacial periods of New Jersey, but so few facts are available that no correlation is 

 possible. 



It is also possible that the Mannetto is a late Tertiary deposit and has no connection or 

 relation to the Pleistocene ice sheets. This seems unlikely since none of the Tertiary deposits 

 of New Jersey resembles the Mannetto. Far too little data on the Mannetto is yet available, to 

 determine its origin, age, or present distribution. It is not possible to identify this formation 

 in well records, or, as a rule in well samples, and it is even uncertain if the surface exposures 

 that have been assigned to the Mannetto do indeed all represent material of the same age. 



This very real uncertainty as to the age and distribution of the Mannetto raises of itself 

 no ground water problem. Where the Mannetto is found it is not found in contact with the 

 below and with upper Pleistocene outwash or till above. It is not found in contact with the 

 Gardiners clay, the Jameco gravel, or the Jacob sand. Under these circumstances it is probably 

 included with the upper Pleistocene in the correlation of well logs, a confusion which is of 

 little direct importance since the sands and gravel of the Mannetto are hydrologically the 

 equivalent of the greater part of the upper Pleistocene and form part of the same hydrologic 

 unit. Indirectly the confusion is unfortunate for an accurate and detailed knowledge of the 

 Mannetto would throw some light on the early Pleistocene history of Long Island, a history 

 which is of great importance in the solution of the broader hydrologic problems. 



The oldest of the undoubted Pleistocene formations on Long Island is the Jameco gravel 

 which in the type area in south-central Queens County extends from about 135 to 250 feet 

 below sea level. The formation is typically about 100 feet thick with its upper surface generally 

 being about 100 feet below sea level. Nowhere does it crop out at the land surface. Locally, 

 where it fills the buried valley segments in southern Kings and Queens Counties, it reaches 

 more than 300 feet below sea level but such depths are uncommon. 



The Jameco gravel underlies all of Kings County except for a belt, a mile or so wide, 

 which parallels the East River. To the east it underlies southern but not central Queens and 

 extends eastward into southern Nassau County. It may extend even farther east along the 

 south shore of the Island but there is not enough data to determine the limit of the formation 

 in this direction. On the northeast, the Jameco gravel probably extends to Flushing Bay in 

 Queens County but how much farther east it may extend and whether it is present at all in 

 northern Nassau and Suffolk Counties is uncertain. One difficulty in determining the bound- 

 aries of the Jameco along the north shore of Long Island results from the possibility of a 

 change in its composition from west to east, and also from a break in the continuity of the 

 deposits. 



The Jameco gravel is easily traced through Kings and western Queens Counties for in 

 this area it forms a continuous deposit and is overlain by a nearly unbroken blanket of Gar- 

 diners clay. In this area also the Jameco gravel contains a large proportion of grains, pebbles, 

 and cobbles of dark diabase (trap) rock similar to that which forms the Palisades of New 

 Jersey. This high proportion of dark rock gives the entire formation a dark color, a charac- 



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