﻿J. 
  W. 
  JVBD 
  ON 
  THE 
  SECONDARY 
  ROCKS 
  OF 
  SCOTLAND. 
  

  

  281 
  

  

  so 
  anomalous 
  as 
  to 
  have 
  occasioned 
  no 
  little 
  difficulty 
  to 
  the 
  older 
  

   geologists 
  who 
  sought 
  to 
  explain 
  them 
  ; 
  indeed 
  the 
  slate 
  rocks 
  were 
  

   found 
  to 
  occcur 
  at 
  such 
  various 
  levels 
  among 
  the 
  series 
  of 
  lavas, 
  con- 
  

   glomerates, 
  and 
  sandstones, 
  and 
  in 
  such 
  unexpected 
  situations, 
  as 
  

   quite 
  to 
  baffle 
  Macculloch 
  and 
  other 
  observers 
  who 
  sought 
  to 
  illustrate 
  

   their 
  relations 
  by 
  horizontal 
  sections*. 
  

  

  That 
  in 
  a 
  district 
  so 
  disturbed 
  as 
  this 
  has 
  been 
  shown 
  to 
  be, 
  the 
  

   strata 
  in 
  question 
  should 
  be 
  found 
  to 
  be 
  traversed 
  by 
  great 
  faults 
  will 
  

   occasion 
  no 
  surprise 
  ; 
  and 
  among 
  rocks 
  of 
  such 
  inconstant 
  characters 
  

   as 
  these, 
  it 
  is, 
  moreover, 
  not 
  easy 
  to 
  detect 
  and 
  follow 
  the 
  details 
  of 
  

   such 
  dislocations, 
  though 
  their 
  general 
  effect 
  may 
  often 
  be 
  sufficiently 
  

   obvious. 
  Thus 
  in 
  the 
  island 
  of 
  Kerrera 
  a 
  N.W. 
  and 
  S.E. 
  fault, 
  with 
  

   a 
  throw 
  of 
  not 
  less 
  than 
  from 
  500 
  to 
  600 
  feet, 
  is 
  very 
  conspicuous. 
  

   It 
  is 
  not, 
  however, 
  to 
  these 
  dislocations, 
  striking 
  as 
  their 
  effects 
  un- 
  

   doubtedly 
  are, 
  that 
  the 
  anomalous 
  position 
  of 
  the 
  rocks 
  in 
  question 
  is 
  

   mainly 
  due, 
  but 
  rather 
  to 
  the 
  fact 
  that 
  the 
  volcanic 
  and 
  associated 
  

   rocks 
  were 
  accumulated 
  upon 
  an 
  old 
  terrestrial 
  surface 
  of 
  great 
  irre- 
  

   gularity, 
  the 
  hills 
  and 
  peaks 
  of 
  which 
  stand 
  up 
  at 
  very 
  various 
  levels 
  

   amidst 
  the 
  great 
  mass 
  of 
  overlying 
  rocks. 
  From 
  the 
  examination 
  of 
  

   the 
  sections 
  near 
  Oban, 
  in 
  the 
  island 
  of 
  Kerrera, 
  and 
  on 
  the 
  shores 
  

   of 
  Lochnell 
  Bay, 
  this 
  relation 
  of 
  the 
  several 
  rocks 
  becomes 
  sufficiently 
  

   clear. 
  Sometimes, 
  in 
  favourable 
  sections, 
  peaks 
  of 
  the 
  Lower 
  Silurian 
  

   slate 
  rocks 
  are 
  actually 
  seen 
  standing 
  up 
  amid 
  the 
  overlying 
  deposits, 
  

   while 
  in 
  other 
  cases 
  hills 
  composed 
  of 
  the 
  former 
  rock 
  stand 
  in 
  such 
  a 
  

   manner 
  amid 
  surrounding 
  masses 
  composed 
  of 
  nearly 
  horizontal 
  beds 
  

   of 
  conglomerate, 
  sandstone, 
  and 
  lava, 
  that 
  no 
  doubt 
  can 
  remain 
  that 
  

   the 
  former 
  constituted, 
  prior 
  to 
  the 
  denudation 
  which 
  has 
  sculptured 
  

   the 
  existing 
  surface, 
  the 
  sides 
  of 
  valleys 
  which 
  were 
  subsequently 
  filled 
  

  

  Fig. 
  9. 
  — 
  Section 
  through 
  the 
  Highest 
  Point 
  of 
  the 
  Island 
  of 
  Kerrera, 
  

   illustrating 
  the 
  Relations 
  between 
  the 
  Slate 
  Rocks 
  and 
  the 
  overlying 
  

   Volcanic 
  Series 
  of 
  Lorn. 
  

  

  a. 
  Lower 
  Silurian 
  slates. 
  b. 
  Breccia 
  composed 
  of 
  angular 
  fragments 
  of 
  a, 
  

   c. 
  Conglomerates 
  and 
  sandstones, 
  d. 
  Porphyrite 
  lava-streams. 
  * 
  Slates 
  

   baked 
  and 
  altered 
  by 
  the 
  enveloping 
  lava. 
  

  

  with 
  the 
  deposits 
  of 
  the 
  latter. 
  Interesting 
  examples 
  of 
  such 
  slate 
  

   hills 
  again 
  exposed 
  by 
  denudation 
  are 
  found 
  at 
  the 
  " 
  mythical 
  Bere- 
  

   gonium" 
  (where 
  the 
  mass 
  is 
  crowned 
  by 
  a 
  vitrified 
  fort) 
  and 
  near 
  

   the 
  town 
  of 
  Oban. 
  The 
  accompanying 
  section 
  (woodcut, 
  fig. 
  9) 
  

  

  * 
  Vide 
  Macculloch's 
  'Western 
  Isles 
  of 
  Scotland,' 
  vol. 
  iii. 
  pi. 
  xvi. 
  fig. 
  3, 
  p. 
  14. 
  

  

  