﻿54 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  studied 
  and 
  hence 
  need 
  not 
  (be 
  considered 
  here. 
  The 
  total 
  thickness 
  

   of 
  Siluric 
  strata 
  along 
  the 
  line 
  of 
  outcrop 
  in 
  the 
  State 
  varies 
  con- 
  

   siderably. 
  In 
  central 
  and 
  western 
  New 
  York 
  the 
  thickness 
  is 
  gen- 
  

   erally 
  from 
  iooo 
  to 
  1500 
  feet, 
  while 
  in 
  southeastern 
  New 
  York 
  it 
  

   is 
  much 
  less 
  since 
  only 
  the 
  thinned 
  upper 
  formations 
  are 
  present. 
  

  

  The 
  first 
  Siluric 
  sediments 
  to 
  form 
  in 
  central 
  and 
  western 
  New 
  

   York 
  are 
  called 
  the 
  Oneida 
  conglomerate 
  and 
  Medina 
  sandstone, 
  

   these 
  two 
  being 
  of 
  practically 
  the 
  same 
  age. 
  These 
  coarse 
  deposits 
  

   were 
  washed 
  into 
  the 
  shallow 
  sea 
  from 
  the 
  northern 
  lands, 
  that 
  is 
  in 
  

   Canada 
  and 
  the 
  Adirondack 
  region. 
  Next 
  in 
  order 
  came 
  the 
  deposits 
  

   of 
  Clinton 
  age, 
  which 
  consist 
  of 
  layers 
  of 
  shale, 
  sandstone 
  and 
  iron 
  

   ore. 
  Above 
  the 
  Clinton 
  come 
  the 
  Lockport 
  and 
  Guelph 
  formations 
  

   made 
  up 
  of 
  shales 
  and 
  dolomitic 
  limestone, 
  the 
  limestone 
  forming 
  the 
  

   crest 
  of 
  Niagara 
  Falls. 
  None 
  of 
  the 
  formations, 
  so 
  far 
  mentioned, 
  

   extend 
  to 
  the 
  Hudson 
  valley, 
  but 
  with 
  the 
  opening 
  of 
  the 
  great 
  Salina 
  

   epoch 
  Siluric 
  deposits 
  for 
  the 
  first 
  time 
  reached 
  to 
  the 
  Hudson 
  valley 
  

   region 
  where 
  the 
  earliest 
  rock 
  to 
  form 
  was 
  the 
  Shawangunk 
  con- 
  

   glomerate 
  which 
  rests 
  upon 
  the 
  eroded 
  Ordovicic 
  shales 
  at 
  the 
  sum- 
  

   mit 
  of 
  Shawangunk 
  mountain. 
  This 
  rock 
  is 
  entirely 
  confined 
  to 
  

   southeastern 
  New 
  York, 
  while 
  rocks 
  of 
  the 
  same 
  age 
  in 
  central 
  and 
  

   western 
  New 
  York 
  are 
  shales 
  and 
  limestones. 
  In 
  this 
  latter 
  region 
  

   the 
  lowermost 
  (oldest) 
  Salina 
  formation 
  is 
  the 
  Vernon 
  red 
  shale, 
  

   usually 
  from 
  100 
  to 
  300 
  feet 
  thick, 
  which, 
  in 
  the 
  western 
  part 
  of 
  

   the 
  State, 
  is 
  overlain 
  by 
  the 
  salt 
  and 
  gypsum 
  beds. 
  Deep 
  wells 
  have 
  

   proved 
  the 
  presence 
  of 
  the 
  salt 
  beds 
  under 
  practically 
  all 
  the 
  South- 
  

   western 
  plateau. 
  The 
  salt 
  was 
  deposited; 
  in 
  great 
  salt 
  lagoons 
  and 
  

   the 
  climate 
  of 
  the 
  time 
  must 
  have 
  been 
  arid. 
  With 
  an 
  influx 
  of 
  

   fresh 
  water 
  into 
  the 
  lagoons, 
  the 
  type 
  of 
  deposit 
  changed, 
  and 
  the 
  

   hydraulic 
  limestone 
  (water 
  lime) 
  beds 
  were 
  formed 
  all 
  the 
  way 
  

   across 
  the 
  State 
  to 
  the 
  Hudson 
  valley 
  region. 
  These 
  water 
  lime 
  

   beds 
  are 
  quarried 
  at 
  many 
  places 
  along 
  the 
  line 
  of 
  outcrop 
  across 
  

   the 
  State, 
  but 
  more 
  especially 
  in 
  the 
  famous 
  Rosendale 
  cement 
  

   region 
  (see 
  plate 
  33). 
  Next 
  in 
  order, 
  and 
  marking 
  the 
  summit 
  of 
  

   the 
  Siluric, 
  come 
  the 
  Cobleskill, 
  Rondout, 
  and 
  Mamlius 
  limestones 
  

   which, 
  though 
  not 
  very 
  thick, 
  are 
  remarkably 
  persistent 
  across 
  the 
  

   State. 
  

  

  As 
  to 
  the 
  life 
  of 
  the 
  Siluric 
  seas 
  it 
  may 
  be 
  said 
  that 
  it 
  is 
  in 
  effect 
  

   the 
  continued 
  existence 
  of 
  the 
  same 
  organic 
  groups 
  that 
  preceded 
  

   in 
  the 
  waters 
  of 
  Ordovicic 
  time, 
  though 
  some 
  diminished, 
  some 
  in- 
  

   creased 
  and 
  some 
  new 
  ones 
  made 
  their 
  first 
  appearance. 
  Thus 
  the 
  

   graptolites 
  and 
  trilobites 
  greatly 
  diminished, 
  while 
  the 
  echinoderms 
  

   (star 
  fishes) 
  increased, 
  and 
  the 
  brachiopods 
  and 
  mollusks 
  held 
  

  

  