﻿OF 
  THE 
  WESTERN 
  ISLES 
  OF 
  SCOTLAND. 
  213 
  

  

  with 
  when 
  the 
  scoriaceous 
  surfaces 
  and 
  upper 
  layers 
  of 
  streams 
  of 
  

   lava 
  have 
  been 
  removed 
  by 
  denudation. 
  But 
  if 
  denudation 
  has 
  done 
  

   so 
  much 
  work 
  on 
  the 
  solid 
  lava-currents, 
  what 
  may 
  we 
  not 
  expect 
  

   it 
  to 
  have 
  effected 
  in 
  the 
  case 
  of 
  cones 
  composed 
  of 
  loose 
  scoriae 
  ? 
  

  

  But 
  other 
  observers 
  who 
  have 
  visited 
  the 
  district, 
  and 
  had 
  far 
  

   greater 
  time 
  and 
  opportunity 
  for 
  studying 
  the 
  phenomena, 
  have 
  come 
  

   to 
  very 
  different 
  conclusions 
  from 
  those 
  which 
  my 
  critic 
  announces. 
  

  

  Captain 
  Raynolcls, 
  one 
  of 
  the 
  earliest 
  explorers 
  of 
  the 
  Snake-River 
  

   district, 
  examined 
  the 
  country 
  in 
  1868, 
  and 
  was 
  accompanied 
  by 
  

   Dr. 
  Hayden, 
  who 
  described 
  volcanic 
  agglomerates 
  as 
  by 
  no 
  means 
  

   wanting 
  in 
  it 
  *. 
  

  

  Dr. 
  Hayden, 
  visiting 
  the 
  district 
  again 
  in 
  1872, 
  found 
  sections 
  

   that 
  proved 
  the 
  basalts 
  not 
  to 
  be 
  massive 
  floods 
  of 
  lava, 
  but 
  thin 
  

   cappmgs 
  overlying 
  beds 
  of 
  trachytic 
  tuff 
  and 
  other 
  rocks, 
  and 
  he 
  

   describes 
  cones, 
  one 
  of 
  them 
  500 
  feet 
  in 
  height, 
  from 
  which 
  these 
  

   lavas 
  seemed 
  to 
  have 
  issued. 
  His 
  descriptions 
  forcibly 
  remind 
  us 
  of 
  

   some 
  portions 
  of 
  the 
  Auvergne 
  f 
  . 
  

  

  At 
  a 
  subsequent 
  date 
  Mr. 
  Clarence 
  King 
  described 
  the 
  basalts 
  of 
  

   the 
  Snake 
  River 
  as 
  being 
  well 
  exposed 
  in 
  the 
  Snake 
  Canon, 
  where 
  

   he 
  found 
  them 
  to 
  consist 
  of 
  thin 
  flows 
  of 
  basalt, 
  superposed 
  one 
  

   upon 
  the 
  other: 
  and 
  the 
  evidence 
  found 
  in 
  the 
  Canon 
  is 
  said 
  to 
  

   distinctly 
  negative 
  the 
  idea 
  that 
  the 
  lava 
  could 
  have 
  flowed 
  from 
  a 
  

   plexus 
  of 
  dykes, 
  inasmuch 
  as 
  such 
  dykes 
  are 
  few 
  in 
  number, 
  and 
  

   sometimes 
  none 
  of 
  them 
  are 
  found 
  for 
  very 
  great 
  distances 
  J. 
  

  

  But 
  in 
  his 
  recent 
  memoir 
  the 
  advocate 
  of 
  " 
  nssure-eruptions" 
  has 
  

   sought 
  to 
  extend 
  the 
  generalization 
  at 
  which 
  he 
  arrived 
  from 
  an 
  

   inspection 
  of 
  the 
  Snake-River 
  basalts 
  to 
  other 
  areas 
  of 
  the 
  Western 
  

   States 
  of 
  America 
  ; 
  and 
  first 
  among 
  these 
  fresh 
  examples 
  he 
  places 
  

   the 
  basalts 
  of 
  the 
  Uinkaret 
  Plateau 
  described 
  by 
  Captain 
  Dutton 
  in 
  

   his 
  admirable 
  work 
  ' 
  The 
  Tertiary 
  History 
  of 
  the 
  Grand 
  Canon 
  

   District.' 
  

  

  Captain 
  Dutton's 
  clear 
  descriptions 
  and 
  Mr. 
  W. 
  H. 
  Holmes's 
  

   beautiful 
  drawings 
  of 
  the 
  scenery 
  of 
  the 
  district 
  give 
  to 
  every 
  

   geologist 
  the 
  opportunity 
  of 
  judging 
  for 
  himself 
  how 
  far 
  the 
  hypo- 
  

   thesis 
  of 
  fissure-eruptions 
  is 
  supported 
  by 
  the 
  district 
  referred 
  to. 
  

   We 
  are 
  told 
  that 
  from 
  one 
  point 
  of 
  view 
  alone 
  the 
  observer 
  may 
  see 
  

   " 
  120 
  to 
  730 
  distinct 
  cinder-cones, 
  and 
  that 
  there 
  are 
  many 
  others 
  

   that 
  will 
  escape 
  detection." 
  Many 
  of 
  these 
  are 
  said 
  to 
  be 
  quite 
  

   small, 
  but 
  others 
  are 
  from 
  700 
  to 
  800 
  feet 
  in 
  height 
  and 
  are 
  a 
  mile 
  

   in 
  diameter 
  §. 
  

  

  The 
  maps 
  |j 
  of 
  the 
  district 
  and 
  the 
  beautiful 
  drawings 
  of 
  Mr. 
  Holmes 
  

   fully 
  confirm 
  this 
  description. 
  The 
  panorama 
  seen 
  from 
  Mount 
  

   Trumbull, 
  where 
  we 
  observe 
  stratiform 
  rocks 
  capped 
  by 
  basalts 
  and 
  

   cut 
  through 
  by 
  streams 
  with 
  later 
  currents 
  of 
  lava 
  issuing 
  from 
  cinder- 
  

  

  * 
  See 
  Captain 
  Raynolds's 
  Eeport, 
  published 
  in 
  1868 
  and 
  1869, 
  chapter 
  x. 
  

   pp. 
  85, 
  &c. 
  ; 
  quoted 
  in 
  U. 
  S. 
  Geol. 
  Surv. 
  of 
  Territories, 
  1872. 
  

  

  f 
  ibid, 
  for 
  1877. 
  

  

  \ 
  U. 
  S. 
  Geol. 
  Explor. 
  of 
  Fortieth 
  Parallel, 
  vol. 
  i. 
  ; 
  Systematic 
  Geology 
  

   pp. 
  672-3. 
  

  

  § 
  Tertiary 
  History 
  of 
  the 
  Grand 
  Canon 
  District 
  (1882), 
  pp. 
  104-112. 
  

  

  || 
  Atlas 
  to 
  accompany 
  the 
  above 
  ; 
  see 
  plates 
  vii., 
  viii., 
  ix. 
  and 
  x. 
  

  

  