teristic that is readily noted in many well logs. This distinctive composition gives added 

 assurance that in western-most Long Island, the gravels which have been assigned to the 

 Jameco do indeed all belong to the same formation. To the east the proportion of diabase 

 apparently decreases and the formation loses this identifying characteristic. 



Along the north shore a second hindrance to the identification of the Jameco gravel is 

 that it would be found only in discontinuous patches because of the very uneven surface of 

 the Cretaceous beds on which it would rest. The Cretaceous surface beneath the peninsulas 

 along the north shore is close to or above sea level, so that the Jameco, which is hardly to be 

 expected at levels higher than 70 or 80 feet below sea level, would only be found underlying 

 the north shore embayments. Gravels which may be of Jameco age do Indeed underlie parts 

 of these embayments but as they are isolated pockets lacking continuity with the type area 

 and have no characteristics which can serve to definitely distinguish them from more recent 

 glacial deposits, their true age is uncertain. 



Earlier reports of studies of the Jameco gravel state or imply that it is older than Wisconsin 

 and most estimates place it as older than Illinoian. If one accepts the correlations and descrip- 

 tions of the pre-Wisconsin glacial deposits of New Jersey where the opportunities to study 

 material of this age are better than they are on Long Island, than the freshness and lack of 

 weathering of the Jameco represents a real problem. The pebbles and mineral and rock grains 

 which it contains are universally described as fresh or only slightly weathered. The Illinoian 

 of New Jersey is described as deeply weathered and the older Jerseyan is even more so. These 

 glacial deposits however are all at or near the surface and are generally above the water table, 

 whereas on Long Island the Jameco gravel is entirely below the water table where it has 

 been subjected to a slower rate of weathering. Whether this difference in location is respon- 

 sible for the striking difference in weathering it is impossible to say but there is a possibility 

 at least that the Jameco gravel is very much younger than has been commonly believed. 



That the Jameco gravel is of glacial origin need not perhaps be questioned but neither 

 has it been proved. The high proportion of boulders of fresh igneous and metemorphic rock 

 points to a rapid and dominantly mechanical attack on the bedrock, which, in an area of 

 moderate relief, suggests the action of frost or glacial ice, but glacial outwash is not the only 

 type of deposit formed of gravel which has been but little weathered. The high proportion of 

 diabase in the formation suggests that the source of at least a large part of the material was to 

 the northwest along the present west bank of the Hudson River. Although it is true that the 

 diabase once was found to the north of Long Island all the way from its present exposures on 

 the Hudson to its present outcrops at New Haven nevertheless by the time the Jameco was 

 formed erosion had reduced the diabase to about its present extent and the source of the diabase 

 in the Jameco must therefore have been in the area that is now New Jersey. 



Although the last ice sheet, and therefore presumably the earlier ones, moved in a direction 

 a little east of south, and so might have carried in some material from the west side of the 

 Hudson, the fact is that diabase is not a major constituent of the post-Jameco tills and outwash 

 in western Long Island. The origin of the Jameco gravel in western Long Island then must 

 in some fashion differ from that of the later outwash deposits since its composition is different. 



One explanation suggested by the very meagre evidence is that the Jameco gravel was 

 deposited by the outwash from a retreating glacier while its ice front lay 20 to 50 miles north 

 of Long Island Sound. At this distance most of the melt water would find its way into the valley 

 of the Hudson where diabase crops out along the west bank of the river. Now at this time the 

 valley of the Hudson was not as deep as it is today, for much of the depth of the present day 

 valley is known to be due to the scour of glacial ice and loaded glacial streams, a process which 

 was then just starting. Not only was the valley floor at a higher level than it is today, but it is 

 probably also safe to assume that sea level was also lower, since a drop in sea level always 



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