586 W. 0. CROSBY 



of a solid, and in the lower part merely a highly viscous, plug of lava 

 by the vertical expansion of less viscous lava beneath, through the 

 separation, due to cooling and relief of pressure, of aqueous and 

 other vapors and various gases. The serpentine relief of Staten 

 Island, on the other hand, is believed to be due to the extrusion (or 

 protrusion) of a plug or stock of serpentine by the vertical expansion 

 resulting from the progressive downward growth of the serpentine 

 through the hydration and consequent swelling of the anhydrous 

 magnesian rock in the alteration of which it has its origin. Reliefs 

 formed after the manner of the Mont Pele obelisk are now known 

 as peleliths; and parity of usage suggests statenliths as an appropriate 

 designation for serpentine reliefs formed on the plan or after the 

 manner of Staten Island Heights. It is, of course, conceivable that 

 a rock formation, antecedent or subsequent, covering a serpentine 

 stock may, by continued upward growth of the latter, be lifted into 

 a dome; and such a dome, somewhat comparable with a laccolithic 

 dome, may be called a statenlithic dome. 



For proof that the statenlith of Staten Island is not unique, a 

 solitary instance, we need look no farther than Castle Point, in 

 Hoboken, between 7 and 8 miles north of Staten Island and approxi- 

 mately on the line of strike of the Staten Island serpentine stock. 

 This point forms a hill about half a mile long and 100 feet high, 

 consisting exclusively of serpentine. It holds the formal relation 

 of a monadnock, not to the Cretaceous peneplain, but to the topo- 

 graphically lower Miocene base-level or partial peneplain very per- 

 fectly developed on the Manhattan schist and Triassic sandstone 

 and shale of Hoboken and Jersey City. That this relatively small 

 serpentine relief, standing on the very brink of the deep, buried 

 gorge of the Hudson, post-dates the base-leveling of the inclosing 

 formations is most probable. It is, thus, essentially similar in its 

 geologic and physiographic relations to the Staten Island serpentine, 

 a parallel instance, and unquestionably a true statenlith. 



The question naturally arises at this point as to whether or not 

 statenliths include only serpentine reliefs; and the answer must be 

 that, on theoretic grounds, at least, various other secondary, 

 hydrous silicates are entitled to recognition, notably the chlorites 

 and probably talc. The chlorites are chiefly derived from augite, 

 hornblende, and biotite; and the total expansion, including acces- 



