﻿HOLMES.] 
  LOWER 
  CRETACEOUS 
  FORMATIONS. 
  261 
  

  

  although 
  it 
  has 
  the 
  same 
  appearance 
  and 
  the 
  same 
  relations 
  to 
  the 
  well 
  

   known 
  Dakota 
  sandstones 
  as 
  the 
  eastern 
  variegated 
  beds, 
  it 
  is 
  not 
  fol- 
  

   lowed 
  by 
  the 
  same 
  well-known 
  Jurassic 
  strata. 
  On 
  the 
  contrary, 
  the 
  

   heavy 
  thickness 
  of 
  peculiar 
  beds 
  which 
  underlie 
  it 
  seem 
  not 
  to 
  be 
  rep- 
  

   resented 
  farther 
  east, 
  and 
  are 
  certainly 
  developed 
  to 
  a 
  greater 
  extent 
  

   here 
  than 
  at 
  any 
  other 
  point, 
  so 
  far 
  as 
  I 
  can 
  learn, 
  west 
  of 
  the 
  mount- 
  

   ains. 
  

  

  In 
  Middle 
  Western 
  Colorado 
  Dr. 
  Peale 
  has 
  found 
  Cretaceous 
  fossils 
  

   in 
  a 
  stratum 
  of 
  sandstone 
  some 
  three 
  or 
  four 
  hundred 
  feet 
  beneath 
  the 
  

   bed 
  of 
  conglomerate, 
  and 
  also 
  beneath 
  a 
  series 
  of 
  variegated 
  beds 
  that 
  

   resemble 
  these 
  in 
  this 
  section. 
  Considering 
  these 
  facts, 
  I 
  cannot 
  do 
  

   better 
  for 
  the 
  present 
  than 
  class 
  this 
  entire 
  series 
  of 
  rocks 
  from 
  the 
  

   level 
  of 
  the 
  Sage 
  Plain 
  to 
  top 
  of 
  the 
  purple 
  laminated 
  beds 
  as 
  Lower 
  

   Cretaceous. 
  Altogether 
  there 
  is 
  a 
  thickness 
  of 
  nearly 
  nine 
  hundred 
  feet, 
  

   only 
  about 
  two 
  hundred 
  feet 
  of 
  which 
  can 
  with 
  absolute 
  certainty 
  be 
  

   said 
  to 
  belong 
  to 
  the 
  Dakota 
  sandstones. 
  These 
  200 
  feet 
  occur 
  at 
  the 
  

   top, 
  and 
  are 
  so 
  distinct 
  from 
  the 
  group 
  beneath 
  that 
  I 
  shall, 
  for 
  con- 
  

   venience, 
  hereafter 
  distinguish 
  them 
  as 
  Upper 
  and 
  Lower 
  Dakota. 
  The 
  

   former 
  consists 
  of 
  two 
  or 
  three 
  beds 
  of 
  massive 
  sandstone 
  or 
  conglom- 
  

   erate, 
  separated 
  by 
  thin 
  layers 
  of 
  shale 
  or 
  marl, 
  that 
  may 
  generally 
  be 
  

   found, 
  where 
  present 
  in 
  a 
  plain 
  country, 
  capping 
  table-lands 
  and 
  form- 
  

   ing 
  long 
  lines 
  of 
  perpendicular 
  cliffs, 
  or, 
  if 
  in 
  the 
  neighborhood 
  of 
  mount- 
  

   ains 
  or 
  abrupt 
  folds, 
  occurring 
  in 
  lines 
  of 
  prominent 
  hog-backs. 
  The 
  

   latter, 
  in 
  the 
  valley 
  of 
  the 
  San 
  Juan, 
  outcrops 
  in 
  the 
  sloping 
  sides 
  of 
  

   the 
  valleys 
  and 
  cartons 
  or 
  in 
  the 
  faces 
  of 
  prominent 
  table-lands, 
  and 
  

   may 
  be 
  distinguished 
  by 
  the 
  total 
  lack 
  of 
  uniformity 
  in 
  weathering, 
  

   composition, 
  and 
  color. 
  

  

  There 
  is 
  a 
  slight 
  rise 
  in 
  the 
  strata 
  north 
  and 
  south 
  from 
  the 
  San 
  Juan. 
  

   From 
  the 
  mouth 
  of 
  Eed 
  Creek 
  to 
  Station 
  45 
  the 
  river-bed 
  seems 
  to 
  be 
  

   in 
  the 
  shallow 
  trough 
  of 
  a 
  synclinal 
  fold. 
  On 
  the 
  south 
  side 
  the 
  dip 
  

   toward 
  the 
  river 
  amounts 
  to 
  from 
  one 
  to 
  three 
  degrees. 
  On 
  the 
  north- 
  

   east 
  side 
  of 
  the 
  Carriso 
  Mountains 
  the 
  Dakota 
  sandstones 
  rise 
  in 
  an 
  un- 
  

   broken 
  slope 
  to 
  the 
  base 
  of 
  the 
  mountains, 
  where 
  they 
  disappear 
  be- 
  

   neath 
  the 
  masses 
  of 
  trachyte. 
  Along 
  the 
  east 
  base, 
  where 
  there 
  has 
  

   been 
  considerable 
  uplifting 
  of 
  the 
  formations, 
  the 
  upper 
  and 
  lower 
  mem- 
  

   bers 
  of 
  the 
  Dakota 
  group 
  have 
  been 
  penetrated, 
  and 
  the 
  red 
  rocks 
  of 
  

   the 
  Jura-Trias 
  are 
  exposed 
  over 
  a 
  considerable 
  area. 
  

  

  West 
  of 
  the 
  valley 
  of 
  Navajo 
  Creek, 
  which 
  has 
  its 
  sources 
  in 
  the 
  

   central 
  part 
  of 
  the 
  Sierra 
  Carriso 
  and 
  reaches 
  the 
  San 
  Juan 
  just 
  below 
  

   the 
  mouth 
  of 
  the 
  Mancos, 
  the 
  Dakota 
  sandstones 
  form 
  an 
  extensive 
  

   sloping 
  table-land, 
  lowest 
  along 
  the 
  San 
  Juan 
  and 
  the 
  highest 
  facing 
  

   the 
  Carriso 
  Mountains. 
  It 
  is 
  separated 
  from 
  these 
  mountains 
  by 
  a 
  wide 
  

   deep 
  valley, 
  which 
  connects 
  the 
  middle 
  portion 
  of 
  the 
  valley 
  of 
  JSTajavo 
  

   Creek 
  with 
  the 
  open 
  country 
  to 
  west 
  about 
  Gothic 
  Creek 
  and 
  the 
  De 
  

   Chelly. 
  Erosion 
  at 
  Navajo 
  Creek 
  has 
  barely 
  reached 
  the 
  laminated 
  

   pur[)lish 
  sandstones, 
  but 
  a 
  little 
  farther 
  west, 
  in 
  the 
  depression 
  occupied 
  

   by 
  Arido 
  Creek, 
  the 
  red-beds 
  are 
  exposed. 
  West 
  of 
  Arido 
  Creek 
  there 
  

   are 
  three 
  or 
  four 
  isolated 
  buttes 
  of 
  red 
  sandstones 
  which 
  present 
  most 
  

   remarkable 
  examples 
  of 
  the 
  "cross-bedding" 
  structure. 
  

  

  The 
  southern 
  face 
  of 
  the 
  sloping 
  mesa 
  which 
  overlooks 
  this 
  valley 
  

   is 
  very 
  regular 
  and 
  continuous, 
  being 
  broken 
  only 
  by 
  the 
  caiion 
  of 
  Arido 
  

   Creek 
  which 
  cuts 
  through 
  it 
  to 
  the 
  San 
  Juan, 
  but 
  the 
  northern 
  border 
  

   which 
  faces 
  the 
  San 
  Juan 
  is 
  extensively 
  broken. 
  The 
  slope 
  to 
  the 
  

   north 
  has 
  turned 
  the 
  drainage 
  all 
  that 
  way, 
  so 
  that 
  a 
  great 
  number 
  of 
  

   long, 
  deep 
  canons 
  reach 
  from 
  the 
  San 
  Juan 
  far 
  back 
  into 
  the 
  table-land. 
  

   On 
  the 
  west 
  this 
  table-land 
  terminates 
  wdth 
  the 
  valley 
  of 
  Desert 
  Creek, 
  

  

  