354 ANNALS NEW YORK ACADEMY OF .SCIENCES 



4). There is also either a conformable or a simple overlap relation be- 

 tween the Inwood and Fordham formations with some interbed- 

 ding of gneiss within the limestone. 



5). The streaked character of the Manhattan schist is due chiefly to 

 igneous impregnation of an already strongly foliated metamorphic 

 rock. Its other characters are of primai-y sources. 



6). The chief impurities of the Inwood, exclusive of the pegmatite dikes, 

 are recrystallized primary niattei's. 



7). The strongly banded structure of the Fordham is of complex origin- 

 its fundamental cause is primary sedimentary difference and strong 

 bedding structure. The rock has been injected along these weak- 

 ness lines with igneous matters. 



8). Distortions are for the most part of regicmal dynamic origin, but in 

 some instances, in the larger intrusives, it is in part of flowage 

 origin. 



9). The prevalent granitic composition of the Fordham is in part of pri- 

 mary (arkose) origin and in iiart simple injection and in ]>art an 

 impregnation of granitizing .solutions. 

 10). There are variations in the Fordham indicative of original inter- 

 bedded limestones similar to the Inwood. and shales similar to the 

 Manhattan, besides the more abundant .sandstones and arkoses. 

 11). There is no direct evidence as to the exact geologic age and no per- 

 fectly satisfactory correlation. 



The Igneous Series: 



12) . The large intrusive masses are represented by : 

 (a) "Yonkers gneiss." 

 (ft) "Raven.swood granodiorite." 



(c) "Staten I.sland serpentine." 



13). The smaller igneous representatives include: 



(d) "Pegmatite dikes." 



(e) "Anthophyllite rock." 



(/) "Hornblende schist strips." 



{g) I^enticular and irregular masses and streaks of pegma- 



titic matter in the schists. 

 (h) Some of the bands of the Fordham gneiss. 

 (i) Much impi-egnating granitic matter now intimately mixed 

 with materials of other origin. 

 14). The principal structui-e of the Yonkers and the Ravenswood is essen- 

 tially primary and of two types : 



(1) A superimposed structure derived from mthI in part pre- 



serving the structure of parti.-illy absorbed older 

 masses. 



(2) An induced structure due to movement in the magmatic 



mass during crysbiUization. 

 15). The structure of the hornblende schist, "Anthophyllite rock" and 



serpentine is chiefly secondary (metamorphic). 

 16). The igneous representatives vary in age. 



