﻿ENDLicH] 
  CONCLUSION 
  — 
  POST-CEETACEOUS. 
  211 
  

  

  ticularly, 
  on 
  the 
  northern 
  drainage 
  of 
  the 
  San 
  Juan, 
  tbat 
  the 
  classifica- 
  

   tion 
  above 
  given 
  finds 
  its 
  most 
  complete 
  application. 
  Descriptions 
  of 
  

   each 
  group 
  are 
  contained 
  in 
  the 
  fourth 
  chapter, 
  which 
  is 
  devoted 
  to 
  that 
  

   region. 
  Viewing 
  the 
  entire 
  system, 
  both 
  Cretaceous 
  and 
  the 
  overlying 
  

   Tertiary, 
  as 
  a 
  whole, 
  we 
  recognize 
  the 
  existence 
  of 
  a 
  Cretaceous 
  inland 
  

   sea, 
  that 
  gradually 
  filled 
  with 
  the 
  material 
  carried 
  to 
  it 
  by 
  the 
  streams 
  

   from 
  which 
  it 
  obtained 
  its 
  waters. 
  Soon 
  after 
  the 
  filling 
  process 
  was 
  

   completed, 
  in 
  part 
  only, 
  vegetation 
  sprang 
  up 
  on 
  the 
  dry 
  land 
  thus 
  

   formed. 
  Local 
  deposits 
  of 
  coal, 
  that 
  frequently, 
  however, 
  extend 
  for 
  a 
  

   number 
  of 
  miles, 
  indicate 
  the 
  boundaries 
  of 
  the 
  former 
  land. 
  Lakes, 
  

   probably 
  of 
  shallow 
  depth 
  only, 
  separated 
  the 
  various 
  regions 
  of 
  land. 
  

   While 
  depositing 
  near 
  their 
  center 
  the 
  shales 
  and 
  marls, 
  the 
  ijroximity 
  

   of 
  sandy 
  shores 
  caused 
  these 
  latter 
  to 
  change 
  and 
  become 
  sandstones. 
  

   This 
  phenomenon 
  at 
  present 
  greatly 
  impedes 
  the 
  progress 
  of 
  a 
  strati- 
  

   graphical 
  geologist, 
  who 
  is 
  accustomed 
  to 
  trace 
  each 
  individual 
  bed 
  as 
  

   such, 
  like 
  the 
  contour 
  of 
  a 
  map. 
  We 
  cannot, 
  therefore, 
  place 
  too 
  much 
  

   reliance 
  upon 
  the 
  recurrence 
  of 
  strata 
  in 
  a 
  formation 
  of 
  this 
  character. 
  

   Eventually 
  the 
  rise 
  of 
  the 
  mountains 
  drained 
  the 
  regions 
  south 
  of 
  them, 
  

   and, 
  flowing 
  off, 
  the 
  water 
  began 
  to 
  cut 
  many 
  narrow 
  valleys 
  and 
  caiions 
  

   through 
  the 
  rapidly-yielding 
  material. 
  Subsequent 
  erosion, 
  aided 
  per- 
  

   haps 
  by 
  seismic 
  action 
  during 
  the 
  volcanic 
  period, 
  increased 
  the 
  depth 
  

   of 
  these 
  caiions, 
  without 
  adding 
  much 
  to 
  their 
  width. 
  Local 
  disturbances 
  

   have 
  produced 
  effects 
  which 
  were 
  taken 
  advantage 
  of 
  by 
  flowing 
  water, 
  

   and 
  we 
  now 
  find 
  valleys 
  where 
  they 
  would 
  certainly 
  not 
  be 
  expected, 
  

   were 
  it 
  not 
  that 
  displacements 
  gave 
  the 
  first 
  impulse 
  to 
  their 
  formation. 
  

  

  Post-Cretaceous. 
  — 
  Chapter 
  five 
  has 
  been 
  devoted 
  to 
  this 
  group, 
  and 
  

   there 
  are 
  stated 
  the 
  essential 
  reasons 
  why 
  the 
  " 
  Lignitic" 
  series 
  should 
  

   not 
  be 
  included 
  either 
  in 
  the 
  older 
  Cretaceous 
  or 
  the 
  younger 
  Tertiary. 
  

   Eegardiug 
  the 
  successions 
  of 
  geological 
  " 
  periods 
  " 
  from 
  an 
  evolutionary 
  

   stand-point, 
  we 
  should 
  expect 
  to 
  find 
  a 
  transition, 
  almost 
  imperceptible, 
  

   so 
  far 
  as 
  organic 
  remains 
  are 
  concerned, 
  from 
  one 
  " 
  formation" 
  to 
  the 
  

   other. 
  As 
  a 
  rule, 
  however, 
  the 
  entire 
  series, 
  as 
  compiled 
  from 
  the 
  lim- 
  

   ited 
  knowledge 
  that 
  we 
  now 
  have 
  of 
  the 
  earth's 
  surface 
  and 
  superficial 
  

   structure, 
  is 
  broken 
  very 
  often 
  on 
  each 
  continent. 
  We 
  find 
  not 
  only 
  

   very 
  abrupt 
  changes 
  in 
  the 
  character 
  of 
  the 
  strata, 
  but 
  in 
  the 
  faunal 
  

   remains, 
  as 
  we 
  pass 
  from 
  one 
  " 
  formation" 
  to 
  another. 
  Forms 
  that 
  we 
  

   have 
  become 
  familiar 
  with 
  in 
  the 
  Jura 
  cease 
  to 
  exist 
  in 
  the 
  Cretaceous, 
  

   while 
  new 
  species 
  and 
  genera 
  are 
  supplied 
  in 
  their 
  stead. 
  Unless 
  we 
  

   choose 
  to 
  accept 
  the 
  hypothesis 
  of 
  " 
  catastrophes," 
  we 
  must 
  assume 
  that 
  

   at 
  the 
  point 
  of 
  observation 
  the 
  formation 
  producing 
  a 
  transition 
  that 
  

   eliminates 
  abrupt 
  termination 
  and 
  beginning 
  is 
  wanting. 
  When 
  we 
  do 
  

   find 
  it, 
  however, 
  we 
  shall 
  expect 
  to 
  see 
  that 
  forms 
  of 
  both 
  the 
  older 
  and 
  

   younger 
  formations 
  to 
  which 
  it 
  is 
  allied 
  will 
  be 
  perpetuated 
  therein. 
  A 
  

   case 
  of 
  such 
  a 
  transition-formation 
  the 
  Post- 
  Cretaceous 
  " 
  Lignitic 
  " 
  

   group 
  offers 
  us. 
  Instead 
  of 
  forcing 
  it 
  into 
  the 
  Cretaceous 
  or 
  Tertiary, 
  

   with 
  neither 
  of 
  which 
  the 
  group 
  fully 
  agrees, 
  I 
  deem 
  it 
  more 
  in 
  con- 
  

   formity 
  with 
  geological 
  science 
  of 
  the 
  present 
  day, 
  and 
  certainly 
  more 
  

   convenient 
  for 
  classificatory 
  purposes, 
  to 
  regard 
  it 
  as 
  an 
  independent 
  

   formation, 
  representing 
  a 
  transition 
  from 
  the 
  Cretaceous 
  to 
  the 
  Tertiary. 
  

  

  Tertiary. 
  — 
  The 
  lowest 
  member 
  of 
  this 
  formation 
  that 
  we 
  find 
  repre- 
  

   sented 
  in 
  our 
  district 
  is 
  the 
  Wasatch 
  group. 
  On 
  the 
  Lower 
  Animas 
  the 
  

   Puerco 
  marls 
  of 
  Cope 
  set 
  in, 
  overlying 
  the 
  Fox 
  Hills 
  beds. 
  Wanting 
  here, 
  

   or 
  very 
  imperfectly 
  developed, 
  is 
  the 
  Lignitic 
  series 
  proper. 
  Above 
  the 
  

   marls 
  massive 
  beds 
  of 
  sandstone 
  set 
  in, 
  continuing 
  southward 
  for 
  a 
  

   long 
  distance. 
  We 
  did 
  not 
  travel 
  far 
  enough 
  in 
  that' 
  direction 
  to 
  

   observe 
  the 
  fossiliferous 
  variegated 
  beds 
  above 
  them. 
  In 
  Chapter 
  

  

  