468 A. A. .TULTEN AMPHIBOLE SCHISTS OF MANHATTAN ISLAND 



zoisite, the theoretical formula. The second line presents the chemical 

 composition of the hornblende schist, as raised to 100 per cent from the 

 analysis by Jouet. 





1^ 



SiOg. 



AI.2O3. 



Feo03. 



FeO. 



MnO. 



CaO. 



MgO. 



KoO. 



Na.,0. 



HoO. 



CO2. 



Chemical composi- 

 tion 





43.62 



17.80 



5.29 



13.23 



.27 



10.17 



6.48 



.40 



1.64 



.37 











Pyrite 



Trace 



.37 



4.92 



.65 



9 08 



1.66 



18.62 



6.24 

























Mjienetite 











.25 



4.92 



.05 



12 

















Hematite 























Biotite 



.26 

 9.08 



.10 









.13 



.08 





.03 

















Calcite 











.93 

 1.81 

 2.33 







"i.'is 





.73 



Labradorite 



10.48 

 2.49 



5.13 



1.42 



.07 









Zoisite 







































22.31 



21.31 

 36.45 

 39.80 



6.65 



11.15 

 19 07 

 14.28 



5.29 



.12 



13.11 

 22.43 

 19.02 



5.07 



5.10 

 8.73 

 10.73 



.13 



6 35 



10.86 



9.10 



.08 



.32 



.55 



2.85 



1.13 



.51 

 .87 

 1.79 



.03 



.34 



.58 



1.42 



.73 





58.46 

 100.00 



.27 

 .46 





XXXIII. 







XXXIV 



2.56 













For comparison, I have appended (XXXIV) the actual analysis by 

 Berwerth of black hornblende (" syntagmatite ") from Vesuvius, to show 

 the identity of our hornblende (XXXIII) in composition with that of 

 volcanic origin. 



DIKE-LIKE LINEAR EXTENSION OF OUTCROPS 



From inspection of scattered exposures of the hornblende schist it 

 might be inferred that if igneous they represent a series of intrusions of 

 limited extent, squeezed up through fissures and mainl}", perhaps, along 

 foliation planes. Many examples of such mode of invasion by a series 

 of short interrupted dikes along the division planes of a stratum have 

 been elsewhere observed — for example, as illustrated by basalt dikes at 

 Cripple creek, Colorado.* Few continuous outcrops of our schist have 

 reached 100 yards in length along the strike. This common limitation, 

 though characteristic of sedimentary lenses, may be otherwise interpreted. 

 There are also some exceptions. Dana states that the thick hornblendic 

 sheet at West One hundred and thirty-fifth street, near Tenth avenue, 

 formerly reached from One hundred and thirty-third to One hundred 

 and thirty-eighth street, over 1,000 feet. The outcrop on Spuyten Duyvil 

 creek may yet be followed for a distance of more than 1,200 feet, and 

 that at East Sixty -fourth street for 800 feet. The tract of amphibole 

 rocks which stretched from West Fifty-fourth to Sixty-third street, near 



*E. A. Stevens, Trans. Am. Inst. Min. Eng., 1903. 



