﻿GEOLOGY 
  OF 
  THE 
  NORTH 
  CREEK 
  QUADRANGLE 
  21 
  

  

  very 
  basic 
  variety 
  may 
  come 
  in 
  and 
  constitute 
  the 
  section 
  for 
  50 
  

   or 
  100 
  feet 
  or 
  more. 
  Yet, 
  while 
  the 
  transition 
  is 
  sharp, 
  there 
  is 
  

   no 
  evidence 
  of 
  separate 
  intrusive 
  masses 
  nor 
  is 
  one 
  justified 
  in 
  

   inferring 
  more 
  than 
  a 
  differentiation 
  of 
  an 
  eruptive 
  mass 
  into 
  

   layers 
  or 
  portions 
  of 
  contrasted 
  composition. 
  . 
  . 
  . 
  That 
  this 
  

   differentiation 
  takes 
  place 
  in 
  magmas 
  is 
  one 
  of 
  the 
  growing 
  con- 
  

   victions 
  of 
  students 
  of 
  igneous 
  rocks." 
  1 
  Now, 
  so 
  far 
  as 
  the 
  

   writer's 
  observations 
  in 
  the 
  North 
  Creek 
  region 
  are 
  concerned, 
  they 
  

   fully 
  accord 
  with 
  Professor 
  Kemp's 
  interpretation 
  of 
  this 
  puzzling 
  

   phenomenon. 
  Of 
  course, 
  the 
  rocks 
  have 
  been 
  severely 
  compressed 
  

   and 
  possibly 
  folded 
  and 
  the 
  banded 
  effect 
  may 
  thus 
  have 
  been 
  ac- 
  

   centuated, 
  but 
  nevertheless 
  there 
  appears 
  to 
  be 
  no 
  getting 
  away 
  

   from 
  the 
  apparent 
  fact 
  of 
  some 
  sort 
  of 
  differentiation 
  of 
  the 
  

   granitic 
  magma 
  into 
  layers 
  of 
  varying 
  composition. 
  

  

  GRANITE 
  PORPHYRY 
  

  

  This 
  rock 
  represents 
  another 
  phase 
  of 
  the 
  great 
  syenite-granite 
  

   intrusive 
  mass 
  and 
  always 
  shows 
  a 
  perfect 
  gradation 
  into 
  either 
  

   the 
  granite 
  or 
  syenite, 
  so 
  that 
  sharp 
  lines 
  of 
  separation 
  between 
  

   these 
  rock 
  types 
  can 
  not 
  be 
  drawn. 
  On 
  the 
  accompanying 
  geologic 
  

   map 
  this 
  rock 
  is 
  seen 
  to 
  be 
  rather 
  widely 
  distributed 
  in 
  small 
  to 
  

   large 
  irregular 
  shaped 
  areas 
  making 
  up 
  altogether 
  perhaps 
  a 
  little 
  

   less 
  than 
  one-ninth 
  of 
  the 
  area 
  of 
  the 
  quadrangle. 
  A 
  very 
  similar 
  

   rock 
  occurring 
  in 
  the 
  vicinity 
  of 
  Northville 
  has 
  recently 
  been 
  de- 
  

   scribed 
  by 
  the 
  writer 
  2 
  and 
  that 
  description 
  applies 
  almost 
  perfectly 
  

   to 
  the 
  North 
  Creek 
  granite 
  porphyry. 
  Exactly 
  the 
  same 
  evidences 
  

   which 
  were 
  presented 
  to 
  prove 
  that 
  the 
  Northville 
  granite 
  porphyry 
  

   is 
  really 
  only 
  a 
  facies 
  or 
  differentiation 
  product 
  of 
  the 
  great 
  syenite 
  

   magma, 
  may 
  also 
  be 
  applied 
  to 
  this 
  granite 
  porphyry. 
  Still 
  more 
  

   recently 
  such 
  rock 
  has 
  been 
  found 
  by 
  the 
  writer 
  in 
  the 
  northern 
  

   portion 
  of 
  the 
  Lake 
  Pleasant 
  quadrangle. 
  Thus 
  it 
  is 
  quite 
  certain 
  

   that 
  granite 
  porphyry 
  is 
  a 
  rather 
  widespread 
  rock 
  in 
  the 
  southeast- 
  

   ern 
  Adirondacks. 
  

  

  The 
  typical 
  rock 
  is 
  gray 
  to 
  pinkish 
  gray, 
  thoroughly 
  gneissoid, 
  

   r.nd 
  with 
  beautifully 
  developed 
  porphyritic 
  texture. 
  The 
  pheno- 
  

   crysts 
  of 
  feldspar 
  are 
  usually 
  from 
  one-half 
  to 
  one 
  inch 
  long 
  and 
  

   more 
  or 
  less 
  flattened 
  parallel 
  to 
  the 
  foliation. 
  Carlsbad 
  twins 
  are 
  

   often 
  easily 
  recognizable. 
  Feldspar, 
  quartz, 
  and 
  biotite 
  or 
  horn- 
  

   blende 
  are 
  always 
  plainly 
  visible 
  to 
  the 
  naked 
  eye. 
  Often 
  large 
  

  

  1 
  N. 
  Y. 
  State 
  Mus. 
  Bui. 
  138, 
  p. 
  48 
  and 
  128. 
  

  

  2 
  N. 
  Y. 
  State 
  Mus. 
  Bui. 
  153, 
  p. 
  17-20. 
  

  

  