PHYSIOGRAPHIC RELATIONS OF SERPENTINE, WITH 



SPECIAL REFERENCE TO THE SERPENTINE STOCK 



OF STATEN ISLAND, N.Y. 



W. O. CROSBY 



Massachusetts Institute of Technology 



The serpentine highland of Staten Island is one of the most 

 anomalous physiographic features of the Cretaceous peneplain of 

 the Atlantic seaboard. This ancient and widespread base-level 

 slopes southeastward and seaward from the highlands of Southern 

 New York and Northern New Jersey; and from the latter district 

 it has been designated, locally, the Schooley Plain. In its approach 

 to the coast it is most continuously and perfectly preserved in the 

 long, straight crest of the Palisade trap ridge. This approach is, in 

 fact, unbroken to Kill Van Kull; and the peneplain passes below 

 sea-level in the northwestern quarter of Staten Island. The 

 normal seaward gradient of the peneplain, in the vicinity of the 

 coast, as proved by numerous deep borings, ranges from 75 to 100 

 feet per mile; and nowhere else is it so perfect and so perfectly 

 preserved as where it is still covered and protected by the Cretaceous 

 sediments beneath which it was progressively buried as it slowly 

 sank below sea-level, and in so sinking received its finishing touches 

 in the addition of marine planation to terrestrial peneplanation. 



Beneath the southeastern and southern plain or lowland of 

 Staten Island, the peneplain, developed here on the Manhattan 

 schists, has been found by the drill at depths (increasing seaward) 

 of 200 to 400 feet, or just where its normal gradient would have led 

 us to expect it. But between the northwestern and southeastern 

 lowlands the continuity of the buried peneplain is interrupted by the 

 great lenticular stock of serpentine nearly eight miles long from 

 northeast to southwest and fully three miles in maximum breadth, 

 and rising to an extreme height of nearly 400 feet above the sea, or 

 400 to fully 800 feet above the encircling peneplain. The south- 

 eastern slope, especially, of this relief is very abrupt and in part 



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