OCCLUSION OF IGNEOUS ROCK 427 



4. Partial leaching out of brucite, magnesite and aragonite 

 into cracks produced by contraction. 



5. Partial alteration of brucite into nemalite, recombination 

 with silica and conversion into marmolite and chrysotile. 



6. Progressive serpentinization of bastite and ainphibole. As 

 in other serpentinoids altered from Iherzolite and wehrlite/ the 

 process here has been selective, attacking successively olivine, 

 orthorhombic pyroxene and monoclinic pyroxene. The ophio- 

 litic alteration of pyroxene has been generally preceded by its 

 initial alteration into uralite or amphibole, the common step in the 

 process throughout the Appalachian belt " as well as abroad.'^ 



Lastly ensued the processes of weathering and partial decom- 

 position of the serpentinoid by cold meteoric waters, with dis- 

 tinct products 



7. Superficial disintegration and dissociation of the rock into 

 ferruginous quartz, colorless, greenish and reddish ^ and into 

 limonite. This action has been deepest at several places on 

 Staten Island. The distinction of the two kinds of siliceous 

 deposits,^ the semicolloidal ( siliciophite of Schrauf ) and the 

 crystalline, near serpentinoid beds, does not appear to have been 

 always recognized. 



8. Occasional slight concentration of chromite, magnetite, and 

 perhaps spinel. 



9. Talcose and chloritic alteration of amphiboles, with sep- 

 aration of lime and magnesia carbonates, in particles and vein- 

 lets of calcite, dolomite and hydromagnesite, with concentration 

 on Manhattan Island, at West 59th Street, as ophicalcite in cavi- 

 ties of the serpentinoid. 



Pegmatite Occlusions on Opposite Side of Hudson River. — 

 The early process of saturation of the schists of Manhattan 



^ J. Ball, The Serpentine and Associated Rocks of Davos, Inaug. Diss., Zurich, 



1897, 15. 



2F. Becke, Sitzber. d. k. Akad. d. IViss., LVI, Beil.-Bnd., Wien, 1867 ; Wil- 

 liams, toe. cit., 45-49, 56-57 ; A. G. Leonard, loc. cit., 163. 



3 Collins, he. cil. , 360. 



* Honeycomb quartz of T. Rand, Proc. Acad. Nat. Sci. Phila., 1880, 241, and 

 1900, 311 ; in Maryland, by decay, the soil known as honeycomb soil, Bascom, loc. 

 cit., 95. 



6 Finckh, loc. cit., 140. 



