GEOLOGY OF THE NEW YORK CITY AQUEDUCT 24 1 



Feet 



135 — i43=Dark micaceous matter containing chiefly biotite, a 

 pearly mica, and quartz. Rock is a decayed schist 

 bed=the transition between Inwood Hmestone and 

 Manhattan schist 



143 — ^i5i=Dark brown micaceous material. Biotite and quartz — 

 chiefly. Rock is decayed schist (transition rock). 

 At 146 feet encountered pieces of a pegmatite veinlet. 

 All pieces except i are pegmatitic — the other one is 

 calcareous sandstone, fallen into this lot from the 

 134 foot level 



151 — i6a=Chunks of pegmatite (a vein rock) 



151 — i6i=The mica washings continue the same as at 143 — 151 

 feet. Rock is a transition schist with pegmatite 

 stringers 



164 — i69=Brownish yellow micaceous matter (loose). Mica, 

 quartz, chlorite, lime. Effervesces 



164 — i73^Many pieces of typical Manhattan schist. A fair 

 amount of core for the conditions. Rock is not so 

 badly decayed but is broken into small pieces. Rock 

 is Manhattan schist of typical character. 



Summary 



1 The material is chiefly river silt down to 46 feet 



2 Lighter glacial deposits 46 — 78 feet 



3 Heavy bouldery drift 78 — 97 feet 



4 Uncertain (insufficient data) 97 — 114 feet 



5 Residuary micaceous decay products from Inwood limestone 



114— 135 feet 



6 Decayed transition schist bed with some lime, but chiefly like the 



Manhattan schist 135 — 161 feet 



7 More calcareous schist 161 — 164 feet 



8 Typical Manhattan schist 164 — 173 feet 



Interpretation 



1 Foreign matters, glacial and recent deposits, continue to a depth 



of between 97 and 114 feet. 



2 Rotten formations (residuary matter) in place begin at least as 



high as 114 feet. There is no foreign material below that point 

 except grains that have fallen into the hole from above. 



