584 W. 0. CROSBY 



Evidently, some other factor than differential erosion is required 

 for a full and satisfactory explanation, especially in the case of such 

 an ancient and pronounced serpentine relief as the Staten Island 

 highland, standing, as it does, in close proximity to the coast and to 

 the mouth of a large river. It is simply inconceivable that with its 

 more complete exposure to the agents of erosion — ^subaerial, fluvial, 

 and marine — the Staten Island serpentine stock should have been 

 able successfully to resist erosion and maintain its high relief 

 throughout the period during which the far harder and more 

 resistant diabase of the nearby Palisade ridge was completely 

 base-leveled. 



The obvious inadequacy of the monadnock or residuary-relief 

 explanation of the serpentine heights of Staten Island has led Willis 

 and Dodge' to explain the relief of the serpentine by faulting. 

 According to this explanation, Staten Island Heights would seem 

 to stand as a solitary instance on our entire Atlantic seaboard of 

 important post-Cretaceous faulting not due to glacial agency; and 

 glacial drag and thrust must be powerless to elevate the bedrock 

 en masse, especially at the extreme limit of the ice invasion. It is, 

 however, further suggested by Willis and Dodge that this supposed 

 faulting may be correlated with that traversing the Newark 

 (Triassic) rocks of New Jersey; although it is commonly conceived 

 that the faults of the Triassic strata date from Triassic time. 

 Were they post-Cretaceous, they could not fail to break the con- 

 tinuity of the Cretaceous peneplain elsewhere than on Staten 

 Island. The suggested faults would be rather unique, also, in 

 closely circumscribing the serpentine area without traversing or 

 breaking the inclosing schist or the Triassic sandstone and trap. 

 Evidently, this explanation is not altogether satisfactory; and it 

 appears advisable to seek further. In fact, we seem forced to the 

 conclusion that the serpentine possesses an inherent power of growth 

 or self-assertion that has enabled it, progressively, to lift its head 

 above the base-level to which it may have been at least approxi- 

 mately reduced in Cretaceous time. 



Assuming, as we must, that this great stock of massive and 

 essentially structureless serpentine has been derived from some 

 massive, basic, and highly magnesian igneous rock, such as peri- 

 ' U.S. Gcol. Survey, Folio 83; Science, February 20, 1903. 



