﻿HYDROLOGY 
  OF 
  NEW 
  YORK 
  685 
  

  

  merit 
  of 
  the 
  area 
  shown 
  by 
  the 
  surface 
  topography 
  to 
  be 
  tribu- 
  

   tary 
  to 
  the 
  proposed 
  point 
  of 
  taking? 
  

  

  3) 
  Is 
  there 
  any 
  geologic 
  reason 
  to 
  expect 
  that 
  the 
  yield 
  

   of 
  ground 
  water 
  available 
  per 
  square 
  mile 
  will 
  be 
  materially 
  

   different 
  in 
  quality 
  or 
  in 
  quantity 
  from 
  that 
  in 
  the 
  region 
  already 
  

   developed 
  west 
  of 
  Massapequa? 
  

  

  4) 
  Is 
  there 
  any 
  apparent 
  advantage 
  in 
  one 
  location 
  over 
  an- 
  

   other 
  for 
  tapping 
  the 
  subterranean 
  waters 
  of 
  the 
  yellow 
  gravel? 
  

  

  The 
  geologic 
  structure 
  of 
  Long 
  Island 
  consists 
  of 
  the 
  follow- 
  

   ing 
  formations, 
  beginning 
  with 
  the 
  lowest: 
  (1) 
  the 
  primitive 
  or 
  

   crystalline 
  rocks; 
  (2) 
  the 
  cretaceous 
  formation; 
  (3) 
  the 
  tertiary 
  

   formation; 
  and 
  (4) 
  the 
  terminal 
  moraine 
  of 
  the 
  continental 
  glacier 
  

   of 
  northeastern 
  North 
  America. 
  

  

  The 
  water-bearing 
  horizons 
  are 
  limited 
  to 
  yellow 
  gravel 
  above 
  

   the 
  blue 
  clay, 
  gray 
  gravel 
  below 
  it 
  and 
  certain 
  layers 
  of 
  sand 
  in 
  

   the 
  cretaceous 
  formation. 
  The 
  yellow 
  gravel, 
  which 
  receives 
  and 
  

   holds 
  nearly 
  the 
  entire 
  rainfall 
  of 
  the 
  island, 
  ranks 
  first 
  in 
  im- 
  

   portance, 
  while 
  the 
  gray 
  gravels 
  and 
  cretaceous 
  gravels 
  are 
  second 
  

   in 
  importance. 
  The 
  supply 
  from 
  the 
  gray 
  and 
  cretaceous 
  gravels, 
  

   if 
  heavily 
  drawn 
  upon, 
  is 
  likely 
  to 
  become 
  brackish, 
  and 
  is 
  also 
  

   likely 
  to 
  become 
  stale 
  or 
  mineralized. 
  

  

  In 
  regard 
  to 
  deep 
  wells, 
  it 
  is 
  stated 
  in 
  Professor 
  Crosby's 
  report 
  

   that 
  while 
  here 
  and 
  there 
  a 
  deep 
  well 
  may 
  tap 
  a 
  supply 
  of 
  good, 
  

   potable 
  water, 
  sufficient 
  for 
  the 
  supply 
  of 
  a 
  small 
  village 
  or 
  

   factory, 
  the 
  geologic 
  formation 
  gives 
  no 
  hope 
  of 
  finding 
  any 
  

   large, 
  permanent 
  deep-well 
  supply 
  sufficient 
  in 
  volume 
  to 
  form 
  a 
  

   substantial 
  increase 
  to 
  the 
  water 
  resources 
  of 
  Brooklyn 
  or 
  add 
  

   materially 
  to 
  the 
  volume 
  that 
  can 
  be 
  obtained 
  from 
  shallow 
  wells. 
  

  

  Before 
  the 
  real 
  facts 
  in 
  regard 
  to 
  tbe 
  geologic 
  formation 
  of 
  

   Long 
  Island 
  were 
  understood 
  it 
  was 
  considered 
  that 
  probably 
  u 
  

   large 
  volume 
  of 
  the 
  fresh 
  water 
  found 
  its 
  way 
  over 
  to 
  Long 
  Island 
  

   from 
  the 
  mainland 
  by 
  percolating 
  through 
  the 
  deep, 
  porous 
  strata, 
  

   but 
  in 
  the 
  light 
  of 
  more 
  extended 
  information 
  Professor 
  Crosby 
  

   considers 
  that 
  whatever 
  yield 
  of 
  fresh 
  water 
  comes 
  from 
  the 
  deep 
  

   wells 
  must 
  have 
  its 
  origin 
  from 
  rain, 
  falling 
  upon 
  Long 
  Island 
  

   alone 
  — 
  there 
  is 
  no 
  water 
  coming 
  to 
  Long 
  Island 
  from 
  the 
  

   mainland. 
  

  

  