The area which is now Long Island was well out on the flank of this arch, so that it was 

 tipped away from the center of the uplift and was lowered rather than raised with respect to sea 

 level. The upraised part of the peneplain to the north and west was quickly attacked by erosion 

 and such streams and rivers as drained the area flowed more rapidly down the newly created 

 slopes to the sea than they had for many millions of years. The sediments which they carried 

 were deposited as the rivers reached the sea, and also on the outer margins of the land where 

 the b.wj.^^ were gentler than they were near the center of the uplift. The area that is now Long 

 Island was near the strand line, sometimes above sea level, sometimes below it, but for the most 

 part it was in a zone of deposition, and hundreds of feet of gravel, sand, and clay accumulated 

 there during the next few million years. These are the Cretaceous sediments, named for the geo- 

 logic period during which they were deposited. The material of which they are composed was 

 derived by the erosion of uplifted portions of the Fall Zone peneplain to the north and west, and 

 the bedrock surface on which they rest is the Fall Zone peneplain itself. 



THE CRETACEOUS SEDIMENTS 



The composition of the Cretaceous sediments tells something of the nature of the Fall Zone 

 peneplain and of the conditions of deposition. The sediments contain, in important amounts, 

 only clay, quartz and muscovite (white mica) . The other minerals such as feldspar, hornblende 

 and biotite (black mica) which were present in the source rock, are not found in the Cretaceous 

 sediments, showing that they had been chemically decomposed by long continued exposure to 

 warmth and moisture. The products of such decomposition are soluble salts, which were no 

 doubt carried away in solution to add their contribution to the salinity of the sea, and clay which 

 is inert and lags behind. This was without question the origin of the clay which forms so large 

 a part of the Cretaceous deposits. The evidence indicates such wide spread and complete decom- 

 position of the bedrock that it seems probable that climatic conditions in the Cretaceous resem- 

 bled the moister parts of the tropics of today where in areas like the Congo and New Guinea, all 

 the rocks, over wide areas, have been decomposed to great depths. 



There are reasons for believing that the material forming the Cretaceous sediments was not 

 transported any great distance. In the first place the divide along the crest of the uparching was 

 not more than 300 miles to the north or west of Long Island. The headwaters of the streams 

 which transported the sediments were situated near this divide. Another reason is the lack of 

 sorting shown by most of the Cretaceous deposits. The beds of sand and gravel contain a large 

 proportion of clay, and many, though not all of the clay beds contain streaks of silt, sand or even 

 gravel. Running water eificiently separates and sorts the material it carries, as shown by the 

 ,presence of thick beds of pure clay or pure sand in many parts of the world. Thus the presence 

 of the two intermixed in beds totaling many hundreds of feet suggests that the water which de- 

 posited them did not travel very far. This intermixing also indicates that the beds were not re- 

 worked after deposition, either by the sea or by the streams which deposited them. 



There is little evidence available to show whether the beds were deposited in the sea, in 

 bays or similar sheltered water, or on low lying river flood plains. Very few fossils have been 

 uncovered in the Cretaceous sediments on Long Island, particularly of the type which would 

 indicate clearly conditions at the time of deposition. 



In all probability the Cretaceous beds were formed along the rather indefinite boundary 

 zone between a low-lying and swampy shore and a coast studded with shallow bays and islands. 

 Rivers from the slightly higher land to the north washed in mud, sand, and some gravel which 

 tended to fill in some of the lakes and swamps on the land and some of the bays and shallow 

 water of the ocean. In New Jersey, where the Cretaceous beds crop out and the opportunity for 

 study is better than on Long Island, the Raritan formation is regarded as a terrestrial deposit 



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