﻿642 
  Forty-seventh 
  Report 
  on 
  the 
  State 
  Museum. 
  

  

  Point, 
  up 
  the 
  valley 
  of 
  Penfield's 
  Pond 
  into 
  central 
  Ticonderoga. 
  

   In 
  southeastern 
  Moriah 
  township 
  the 
  Potsdam 
  reaches 
  an 
  alti- 
  

   tude 
  of 
  600 
  feet 
  above 
  tide. 
  The 
  rocks 
  of 
  III 
  from 
  the 
  high 
  

   peaks 
  of 
  the 
  interior, 
  where 
  in 
  the 
  group 
  about 
  Mt. 
  Marcy 
  they 
  

   have 
  their 
  greatest 
  development. 
  They 
  extend 
  to 
  the 
  north, 
  

   however, 
  beyond 
  the 
  limits 
  of 
  Essex 
  county, 
  for 
  A. 
  S. 
  Eakle 
  has 
  

   mentioned 
  them 
  near 
  Upper 
  Chateaugay 
  lake 
  (Amer. 
  Geol., 
  

   July, 
  1893, 
  p. 
  32), 
  and 
  N. 
  L. 
  Britton 
  has 
  noted 
  their 
  presence 
  at 
  

   Lower 
  Saranac 
  lake, 
  just 
  west 
  of 
  the 
  Essex 
  line 
  in 
  Franklin 
  county. 
  

   (Trans. 
  1ST. 
  Y. 
  Acad. 
  Sci., 
  Yol. 
  V, 
  p. 
  72, 
  1886.) 
  Prof. 
  Gushing 
  has 
  

   also 
  found 
  gabbro 
  along 
  the 
  line 
  of 
  Beekmantown-Altona, 
  north- 
  

   west 
  of 
  Plattsburgh. 
  The 
  tracing 
  of 
  the 
  northern 
  and 
  western 
  

   limits 
  of 
  these 
  rocks 
  will 
  be 
  a 
  most 
  important 
  and 
  interesting 
  

   addition 
  to 
  our 
  knowledge. 
  

  

  The 
  evidence 
  of 
  their 
  intrusive 
  character 
  and 
  later 
  geological 
  

   age 
  than 
  I 
  and 
  II, 
  may 
  be 
  summed 
  up 
  as 
  follows 
  : 
  

  

  A. 
  They 
  are 
  composed 
  of 
  minerals 
  characteristic 
  of 
  the 
  gabbro- 
  

   group. 
  They 
  exhibit 
  a 
  massive 
  habit 
  in 
  the 
  larger 
  mountain 
  

   masses, 
  where 
  they 
  find 
  their 
  best 
  and 
  least 
  altered 
  development. 
  

   The 
  anorthosites 
  or 
  richer 
  feldspathic 
  varieties 
  are 
  somewhat 
  

   abnormal 
  when 
  compared 
  with 
  gabbros 
  the 
  world 
  over, 
  but 
  are 
  

   practically 
  identical 
  with 
  those 
  of 
  Canada, 
  where 
  these 
  rocks 
  

   have 
  an 
  even 
  greater 
  development 
  than 
  in 
  the 
  Adirondacks. 
  In 
  

   the 
  same 
  ridge 
  we 
  find 
  the 
  typical 
  anorthosites 
  and 
  basic 
  olivine- 
  

   gabbros 
  as 
  phases 
  of 
  the 
  same 
  magma 
  (Split. 
  Eock 
  mountain). 
  

  

  B. 
  Except 
  where 
  a 
  gneissoid 
  facies 
  has 
  been 
  developed, 
  they 
  

   exhibit 
  typical 
  granitoid 
  structure, 
  and 
  a 
  gradual 
  passage 
  may 
  be 
  

   traced 
  in 
  the 
  same 
  mass 
  from 
  this 
  into 
  the 
  gneissoid 
  type. 
  The 
  

   latter 
  is 
  chiefly 
  found 
  in 
  the 
  outlying 
  ridges. 
  

  

  C. 
  The 
  smaller 
  outliers 
  are 
  basic 
  gabbro, 
  but 
  as 
  they 
  are 
  just 
  

   the 
  same 
  rock 
  as 
  the 
  more 
  basic 
  developments 
  in 
  the 
  main 
  masses, 
  

   we 
  are 
  justified 
  in 
  grouping 
  all 
  together 
  as 
  a 
  single 
  geological 
  

   unit. 
  These 
  outliers 
  penetrate 
  the 
  gneisses 
  and 
  crystalline 
  lime- 
  

   stones 
  as 
  dikes, 
  of 
  no 
  great 
  width, 
  in 
  Ticonderoga 
  (near 
  Long 
  

   pond, 
  Spec. 
  365, 
  352, 
  316, 
  347), 
  as 
  numerous 
  knobs 
  in 
  many 
  

   localities, 
  and 
  as 
  great 
  intrusions 
  of 
  especial 
  interest 
  just 
  north 
  

   of 
  Port 
  Henry. 
  At 
  the 
  Cheever 
  mine 
  the 
  typical 
  massive 
  gabbro, 
  

   underlies 
  the 
  normal 
  gneiss 
  which 
  forms 
  the 
  footwall 
  of 
  the 
  ore 
  

   upon 
  which, 
  after 
  a 
  hanging 
  wall 
  of 
  gneiss, 
  is 
  found 
  the 
  crystal- 
  

  

  