SERPENTINE OUTCROPS 489 



From Sixth to Eighth and Ninth avenues thinly bedded micaceous 

 gneiss, highly quartzose, with thin alternations of compact gneiss and 

 mica schist. 



From Ninth avenue the same gneiss for about 250 feet, with micaceous 

 la3^ers, often wavy, followed by four layers of slaty hornblende schist, 

 about 100 feet, separated by thin sheets of coarse granitoid gneiss ; then 

 gray gneiss, with equal amounts of white and black micas, as far as Tenth 

 avenue, inclosing a thick bed of coarse pegmatite carrying large crystals 

 of orthoclase and muscovite. 



From Tenth avenue micaceous gneiss, 250 feet ; mica schist, nearly 

 80 feet ; blackish green tremolitic serpentine (spotted with greenish gray 

 altered actinolite), about 40 feet, inclosing thin sheets of tremolite schist ; 

 hydrated tremolite schist ('' h3^drous anthophyllite "), at least 60 feet, 

 inclosing many layers and amorphous masses of serpentine, ophicalcite, 

 compact tremolite rock, and sometimes asbestus. Strike undisturbed ; 

 dip 70° west. 



From Eleventh avenue, again the micaceous gneiss, inclosing one thin 

 layer of mica schist, as far as the shore of the Hudson river, about 

 Twelfth avenue ; same strike and dip. 



The section has been presented in this detail to explain the uniform 

 continuity of the bedding, those of tremolite, serpentine, etcetera, occu- 

 pying a position toward the upper part of the stratum, so far as present 

 in the section ; also the frequent intercalation of hornblende schists and 

 granite sheets. The la3^ers of hydrous magnesian rocks between Tenth 

 and Eleventh avenues were plainly derivatives from an original heavy 

 bed of actinolite schist, about 100 feet. If a reversed fold, common on 

 the island, occurred here, between Ninth avenue and the river, this bed of 

 actinolite schist between Tenth and Eleventh avenues was but a facies 

 of the thick bed of hornblende schist between Ninth and Tenth avenues ; 

 but in the absence of any evidence of such a fold, I was more inclined 

 to the view that this actinolitic bed and its derivatives corresponded to 

 the upper hornblendic la3^er, that which occurred as a tremolite bed at 

 Fifty-ninth street and Sixth avenue. 



As for the purest rock serpentine here, it was but a serpentinized tremo- 

 lite rock, such as classed by von Drasche under " serpentine-like rocks." '-^ 

 On account of its softness, however, such portions of the bed had under- 

 gone a deeper decay and subsequent scoring out by glacier action. 

 Doctor Gale states that he found the more resistant " anthophyllite 

 rock " occup3dng " a series of conical hills — some five or six — in a north- 

 erly and southerh^ direction." f 



*Tsch. min. u. pet. Mitth., 1871, p. 1. 

 t Mather, op. cit., pp. 92, 94. 



