﻿1 
  8 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  times 
  the 
  evidence 
  seems 
  conclusive 
  that 
  Grenville 
  gneisses 
  

   have 
  been 
  melted 
  and 
  actually 
  assimilated 
  by 
  the 
  molten 
  intru- 
  

   sions 
  so 
  that 
  various 
  rocks 
  of 
  intermediate 
  character 
  have 
  

   resulted. 
  

  

  Only 
  a 
  few 
  diabase 
  and 
  gabbro 
  dikes 
  have 
  been 
  found. 
  Several 
  

   of 
  the 
  diabase 
  dikes 
  are 
  distinctly 
  porphyritic 
  with 
  large 
  plagio- 
  

   clase 
  crystals, 
  but 
  the 
  exact 
  nature 
  of 
  these 
  rocks 
  has 
  not 
  yet 
  

   been 
  determined. 
  

  

  The 
  chief 
  geologic 
  interest 
  of 
  the 
  quadrangle 
  centers 
  about 
  

   the 
  valley 
  at 
  Wells 
  because 
  of 
  the 
  location 
  there 
  of 
  the 
  important 
  

   outlier 
  of 
  Paleozoic 
  rocks 
  comprising 
  Potsdam 
  sandstone, 
  

   Theresa 
  passage 
  beds, 
  Little 
  Falls 
  dolomite, 
  Black 
  River 
  (Low- 
  

   ville) 
  limestone, 
  Trenton 
  limestone, 
  and 
  Canajoharie 
  (Trenton) 
  

   black 
  shale. 
  Altogether 
  the 
  thickness 
  of 
  these 
  strata 
  is 
  about 
  

   five 
  hundred 
  feet 
  and 
  their 
  areal 
  extent 
  about 
  three 
  square 
  miles. 
  

   The 
  valley 
  is 
  of 
  the 
  nature 
  of 
  a 
  fault 
  basin 
  with 
  distinct 
  faults 
  

   along 
  the 
  eastern 
  and 
  western 
  sides 
  and 
  a 
  minor 
  one 
  between. 
  

   Along 
  the 
  western 
  side 
  of 
  the 
  outlier 
  the 
  displacement 
  of 
  the 
  

   fault 
  is 
  no 
  less 
  than 
  2000 
  feet, 
  the 
  Canajoharie 
  shales 
  showing 
  a 
  

   decided 
  updrag 
  effect 
  near 
  the 
  fault. 
  A 
  very 
  careful 
  survey 
  of 
  

   the 
  vicinity 
  of 
  Wells 
  has 
  been 
  made 
  resulting 
  in 
  the 
  first 
  detailed 
  

   areal 
  map 
  (with 
  structure 
  sections) 
  of 
  this 
  the 
  most 
  interesting 
  

   Paleozoic 
  rock 
  outlier 
  in 
  the 
  Adirondacks. 
  

  

  Another 
  feature 
  of 
  special 
  interest 
  is 
  the 
  discovery 
  of 
  an 
  out- 
  

   lier 
  of 
  Paleozoic 
  rock 
  in 
  the 
  Sacandaga 
  valley 
  from 
  one 
  to 
  two 
  

   miles 
  above 
  Hope 
  post 
  office. 
  The 
  only 
  strata 
  visible 
  are 
  con- 
  

   siderable 
  ledges 
  of 
  Little 
  Falls 
  dolomite 
  and 
  a 
  little 
  of 
  the 
  

   Theresa 
  passage 
  beds 
  and 
  Black 
  River 
  limestone. 
  These 
  strata 
  

   are 
  sharply 
  downfaulted 
  at 
  least 
  1200 
  feet 
  against 
  the 
  steep 
  

   mountain 
  on 
  the 
  western 
  side 
  of 
  the 
  valley. 
  A 
  minor 
  fault 
  

   appears 
  to 
  bound 
  this 
  outlier 
  on 
  the 
  east 
  so 
  that 
  this 
  too 
  seems 
  

   to 
  be 
  a 
  fault 
  basin. 
  

  

  The 
  major 
  topographic 
  features 
  of 
  the 
  quadrangle 
  are 
  largely 
  

   determined 
  by 
  normal 
  faults, 
  most 
  of 
  which 
  strike 
  northeast- 
  

   southwest, 
  though 
  certain 
  important 
  cross 
  faults 
  also 
  occur. 
  

   There 
  are 
  many 
  good 
  examples 
  of 
  fault 
  blocks, 
  ridges 
  and 
  

   basins. 
  

  

  Glacial 
  striae 
  show 
  the 
  movement 
  of 
  the 
  great 
  ice 
  sheet 
  to 
  

   have 
  been 
  southward 
  to 
  southwestward. 
  There 
  are 
  several 
  fine 
  

   examples 
  of 
  extinct 
  glacial 
  lakes, 
  especially 
  those 
  in 
  the 
  valley 
  

   at 
  Wells 
  ; 
  along 
  the 
  Sacandaga 
  river 
  between 
  the 
  mouth 
  of 
  the 
  

  

  