﻿130 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  platforms 
  are 
  well 
  shown 
  on 
  both 
  the 
  Theresa 
  and 
  Alexandria 
  

   sheets. 
  

  

  Though 
  the 
  Potsdani 
  as 
  a 
  whole 
  is 
  strong, 
  the 
  uppermost 
  beds, 
  

   together 
  with 
  the 
  sand 
  beds 
  in 
  the 
  basal 
  Theresa, 
  form 
  a 
  weak 
  com- 
  

   bination, 
  in 
  which 
  the 
  massive 
  bed 
  of 
  the 
  Potsdam 
  summit 
  is 
  rela- 
  

   tively 
  strong. 
  The 
  overlying 
  Theresa 
  is 
  also 
  stronger 
  than 
  this 
  weak 
  

   zone, 
  and 
  hence 
  the 
  Theresa 
  edges 
  form 
  rather 
  prominent 
  infaces, 
  

   with 
  these 
  weak 
  beds 
  at 
  their 
  base 
  ; 
  not 
  infrequently 
  also 
  the 
  strong 
  

   summit 
  bed 
  of 
  the 
  Potsdam 
  forms 
  a 
  narrow 
  platform 
  of 
  its 
  own, 
  

   part 
  way 
  up 
  the 
  inface 
  [pi. 
  33]. 
  The 
  Theresa 
  rocks 
  weather 
  to 
  

   iron 
  stained 
  crusts 
  and 
  their 
  exposed 
  edges 
  have 
  a 
  thin 
  -bedded 
  

   look, 
  giving 
  these 
  infaces 
  a 
  peculiar 
  and 
  unmistakable 
  look 
  of 
  

   their 
  own. 
  Above 
  the 
  base 
  the 
  Theresa 
  shows 
  rather 
  rapid 
  alter- 
  

   nations 
  of 
  thicker 
  and 
  thinner 
  bedded 
  layers, 
  the 
  former 
  somewhat 
  

   more 
  resistant, 
  so 
  that 
  low 
  infaces 
  of 
  these, 
  various 
  layers 
  are 
  fre- 
  

   quent 
  throughout 
  the 
  Theresa 
  country. 
  

  

  The 
  sandy 
  basal 
  layers 
  of 
  the 
  Pamelia 
  formation, 
  some 
  25—30 
  feet 
  

   thick, 
  constitute 
  the 
  weakest 
  zone 
  within 
  our 
  map 
  limits, 
  and 
  are 
  

   readily 
  stripped 
  awa}- 
  from 
  the 
  Tribes 
  Hill 
  underneath, 
  while 
  the 
  

   overlying 
  limestone 
  is 
  more 
  resistant, 
  so 
  it 
  is 
  not 
  surprising 
  that 
  the 
  

   Pamelia 
  cliff 
  front 
  is 
  one 
  of 
  the 
  most 
  conspicuous 
  topographic 
  fea- 
  

   tures 
  of 
  the 
  district, 
  a 
  feature 
  which 
  the 
  contour 
  maps 
  clearly 
  bring 
  

   out. 
  In 
  front 
  lies 
  a 
  flat 
  Tribes 
  Hill 
  platform. 
  The 
  cliff 
  ranges 
  from 
  

   20 
  feet 
  to 
  more 
  than 
  100 
  feet 
  in 
  hight, 
  but 
  is 
  usually 
  from 
  50 
  to 
  60. 
  

   Higher 
  up 
  in 
  the 
  formation 
  the 
  occasional 
  very 
  massive 
  limestone 
  

   beds 
  form 
  frequent 
  low 
  infaces 
  of 
  their 
  own, 
  as 
  in 
  the 
  case 
  of 
  the 
  

   Theresa 
  formation. 
  The 
  Lowville 
  differs 
  but 
  little 
  from 
  the 
  Pamelia 
  

   in 
  resistance, 
  and 
  has 
  no 
  zone 
  of 
  weakness 
  at 
  its 
  base, 
  hence 
  is 
  not 
  

   fronted 
  by 
  a 
  prominent 
  inface 
  of 
  its 
  own, 
  and 
  is 
  the 
  only 
  formation 
  

   which 
  -lacks 
  one. 
  It 
  has 
  its 
  own 
  minor 
  fronts, 
  but 
  these 
  are 
  of 
  the 
  

   same 
  order 
  of 
  magnitude 
  as 
  those 
  of 
  the 
  upper 
  PameHa 
  beneath. 
  

  

  The 
  Leray 
  is 
  a 
  thin 
  formation, 
  but 
  because 
  of 
  the 
  massive- 
  

   ness 
  of 
  its 
  beds, 
  and 
  the 
  abundance 
  of 
  chert 
  in 
  its 
  lower 
  portion, 
  it 
  

   everywhere 
  forms 
  infaces 
  with 
  distinct 
  characters 
  of 
  their 
  own, 
  of 
  

   which 
  the 
  curious 
  blocky 
  type 
  of 
  weathering 
  is 
  the 
  most 
  conspicuous 
  

   [pi. 
  20]. 
  The 
  7 
  foot 
  tier 
  above 
  also 
  has 
  a 
  front 
  of 
  its 
  own. 
  

  

  The 
  thin 
  bedded 
  Trenton 
  limestone 
  is 
  considerably 
  less 
  resistant 
  

   than 
  the 
  Watertown, 
  hence 
  the 
  ^^'atertown 
  platform 
  in 
  front 
  of 
  the 
  

   Trenton 
  inface 
  is 
  comparatively 
  broad, 
  especially 
  when 
  the 
  small 
  

   thickness 
  of 
  the 
  formation 
  is 
  taken 
  into 
  consideration. 
  Notwith- 
  

   standing 
  the 
  weakness 
  of 
  the 
  Trenton, 
  its 
  inface 
  to 
  the 
  south 
  of 
  

   the 
  Black 
  river 
  is 
  far 
  the 
  highest 
  and 
  most 
  commanding 
  of 
  the 
  

  

  