590 W. 0. CROSBY 



limited to the periphery of the serpentine stock and to the kata- 

 morphic zone, finds its origin in the quiet and unobtrusive chemical 

 reactions of that zone involved in the secular absorption and down- 

 ward penetration of meteoric water, and the displacement must, 

 obviously, die out downward. 



Apparently, then, we have in the statenlith not only a new 

 physiographic type, but also, in its periphery, a hitherto unrecog- 

 nized type of fault, a type finding its origin in the localized, deep- 

 seated expansion, through hydration, of the base of the upthrow 

 block. Assuming that the horizontal dimensions of the statenlith 

 increase downward, the encircling fault would be, structurally at 

 least, of the normal or gravity type. 



Pursuing this subject a step further, and recognizing that 

 reversed or thrust faults are due to horizontal compression, that 

 normal or gravity faults are due to vertical compression, and 

 that vertical compression can yield only normal faults, we may, on 

 genetic grounds, distinguish two types of normal faults: first, those 

 due to the gravitative settling of the hanging wall block; and, 

 second, those due to the upward expansion of the footwall block. 

 The expansion of the footwall may be, in varying proportions, both 

 thermal and aqueous, that is, due to the absorption of heat and of 

 water, the normal fault of this type being the precise geologic con- 

 comitant of the statenlith. 



On passing now to the consideration of the relations of the 

 Staten Island statenHth to the history of the Coastal Plain, of which 

 it is one of the most commanding relief features, we are confronted 

 at the outset with the question as to whether or not the statenhth's 

 innate power of topographic rejuvenation has enabled it to keep its 

 head above water throughout Cretaceous and Tertiary times, thus 

 making it a perpetual watch tower guarding the mouth of the 

 Hudson. Although continuity of rehef through geologic ages, a 

 sort of physiographic immortaHty, is conceivable, it is, nevertheless, 

 highly improbable. The clearest disproof of topographic per- 

 petuity would, of course, be afforded by overlying Coastal Plain 

 sediments; but this evidence, unfortunately, is almost wholly 

 wanting; although its absence proves nothing to the contrary. 



The only sediment referable to the Coastal Plain series now 

 resting upon the Staten Island serpentine is the yellow gravel 



