﻿162 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  Although 
  evaporation 
  played 
  an 
  important 
  part 
  in 
  the 
  fluctua- 
  

   tions, 
  so 
  far 
  as 
  appears 
  from 
  the 
  report, 
  this 
  element 
  was 
  not 
  

   taken 
  into 
  account 
  in 
  drawing 
  the 
  foregoing 
  conclusions. 
  

  

  The 
  error 
  in 
  precipitation, 
  due 
  to 
  not 
  fully 
  taking 
  into 
  account 
  

   the 
  amount 
  of 
  snow, 
  should 
  also 
  be 
  considered. 
  

  

  Relation 
  of 
  Geologic 
  Structure 
  to 
  Runoff 
  

  

  Among 
  the 
  principal 
  factors 
  affecting 
  stream 
  flow 
  should 
  

   be 
  noted 
  the 
  structure 
  and 
  texture 
  of 
  the 
  rocks, 
  specially 
  

   those 
  of 
  the 
  surface. 
  For 
  example, 
  in 
  regions 
  with 
  stiff, 
  heavy, 
  

   clay 
  soils, 
  a 
  larger 
  proportion 
  of 
  the 
  winter 
  rainfall 
  runs 
  off 
  

   on 
  the 
  surface, 
  passing 
  immediately 
  into 
  the 
  streams, 
  than 
  

   is 
  the 
  case 
  in 
  regions 
  with 
  open, 
  porous 
  soils 
  or 
  extensive 
  

   sandy 
  areas, 
  while 
  in 
  summer 
  a 
  much 
  smaller 
  proportion 
  runs 
  

   off. 
  But 
  such 
  streams 
  have 
  a 
  very 
  much 
  smaller 
  ground- 
  

   water 
  flow, 
  from 
  whence 
  it 
  results 
  that 
  the 
  total 
  runoff 
  per 
  

   year 
  is 
  smaller 
  than 
  for 
  streams 
  with 
  open, 
  sandy 
  soils. 
  

   The 
  Genesee 
  and 
  Hudson 
  rivers 
  represent 
  the 
  extremes 
  of 
  

   the 
  State 
  in 
  this 
  particular. 
  A 
  general 
  knowledge 
  of 
  the 
  

   surface 
  geology 
  is 
  therefore 
  desirable 
  in 
  a 
  study 
  of 
  the 
  water 
  

   resources 
  of 
  the 
  iState. 
  The 
  relative 
  position 
  and 
  area 
  of 
  the 
  dif- 
  

   ferent 
  geologic 
  formations 
  are 
  best 
  shown 
  on 
  the 
  large 
  Geologic 
  

   Map 
  of 
  New 
  York 
  prepared 
  by 
  Dr 
  F. 
  J. 
  H. 
  Merrill, 
  State 
  Geolo- 
  

   gist, 
  in 
  1901 
  (scale 
  5 
  miles 
  to 
  the 
  inch) 
  . 
  A 
  similar 
  but 
  smaller 
  map 
  

   by 
  the 
  same 
  author, 
  showing 
  essentially 
  the 
  same 
  features 
  was 
  also 
  

   printed 
  in 
  1894 
  under 
  authority 
  of 
  uhe 
  Regents 
  of 
  the 
  University 
  to 
  

   accompany 
  the 
  Report 
  on 
  the 
  Mineral 
  Exhibit 
  of 
  New 
  York 
  at 
  the 
  

   World's 
  Columbian 
  Exposition, 
  this 
  being 
  on 
  the 
  scale 
  of 
  approxi- 
  

   mately 
  14 
  miles 
  to 
  an 
  inch. 
  This 
  map 
  was 
  also 
  published 
  with 
  

   Bulletin 
  15 
  of 
  the 
  State 
  Museum 
  and 
  was 
  reproduced 
  in 
  1901 
  by 
  

   Edward 
  A. 
  Bond, 
  State 
  Engineer, 
  in 
  his 
  report 
  on 
  the 
  proposed 
  

   barge 
  canal. 
  On 
  examining 
  either 
  of 
  these 
  maps 
  one 
  will 
  note 
  

   the 
  preponderance, 
  so 
  far 
  as 
  area 
  is 
  concerned, 
  of 
  two 
  classes 
  of 
  

   rocks 
  — 
  the 
  ancient 
  crystallines, 
  which 
  cover 
  a 
  large 
  area 
  in 
  the 
  

   northern 
  part 
  of 
  the 
  State, 
  and 
  the 
  conglomerates, 
  sandstones 
  and 
  

   shales 
  of 
  the 
  Devonian, 
  which 
  form 
  the 
  greater 
  part 
  of 
  the 
  Appa- 
  

   lachian 
  plateau 
  ; 
  stretching 
  from 
  Lake 
  Erie 
  across 
  the 
  State 
  to 
  

  

  