GEOLOGY OF THE NEW YORK CITY AQUEDUCT 243 



Hole no. 42 (75 feet from Speedway, 25 feet east of hole no. 17) 



Feet 



o to -94.1 River muds and various types of drift similar to 

 hole no. 17 

 -94 to —96 Iron cemented sand — both drift sand and local 



angular material 

 -98 to -127 Micaceous clay — residuary decayed matter — 

 with choppings of calcite, quartz, mica and 

 chlorite representing weathered Inwood lime- 

 stone 



-127 to -135 Core — Inwood limestone (impure) 



-135 to -149.5 Pegmatite 



-149.5 to -197 Inwood limestone — typical — standing almost 

 vertical in upper portion but changing to about 

 45° and farther down to 60°. Good sound 

 rock 



-197 to -241 Manhattan schist — of typical sort — and in 

 sound condition, but becoming somewhat more 

 broken and altered near the bottom. Dip about 

 6o°-8o° and even more. Average probably 

 75°-8o° 



-241 to -295 Manhattan schist — typical — dip variable but 

 mostly above 70° to vertical — some pegmatite 

 — fractures are at high angle. Rock sound 



-295 to -302.5 Pegmatite 



-302.5 to -442.7 Inwood limestone — typical — good quality — dip 

 70° to very flat — one piece not over 35° but 

 mostly obscure 

 An interpretation summary is as follows: 



Feet 



o to -94 River muds and drift filling (glacial and recent) 

 -94 to -96 Transition to residuary matter 



-96 to -127 Residuary matter and badly decayed Inwood lime- 

 stone 

 -127 to -197 Inwood limestone 

 -197 to -302 Manhattan schist 

 -302 to -442.7 Inwood limestone 



Geologic cross section. The accompanying cross section 

 [pi. 35] embodies an interpretation of all the data secured m ihe 

 Plarlem river. It is now known that the limestone is overturned 



