﻿J. 
  W. 
  JUDD 
  ON 
  TEE 
  SECONDARY 
  ROCKS 
  OF 
  SCOTLAND. 
  229 
  

  

  streams, 
  but 
  without 
  the 
  interesting 
  accompaniments 
  of 
  the 
  leaf- 
  

   beds 
  and 
  entangled 
  chalk 
  detritus 
  which 
  occur 
  at 
  Ardtun, 
  have 
  been 
  

   found 
  by 
  me 
  in 
  various 
  parts 
  of 
  the 
  Hebrides. 
  An 
  example 
  of 
  a 
  

   very 
  thick 
  mud-stream 
  buried 
  under 
  lava 
  occurs 
  on 
  the 
  shores 
  of 
  

   Loch 
  Tuadh 
  in 
  Mull, 
  opposite 
  to 
  the 
  adjoining 
  island 
  of 
  Ulva. 
  

  

  (4) 
  Professor 
  Geikie 
  has 
  called 
  attention 
  to 
  the 
  existence 
  at 
  the 
  

   Innimore 
  of 
  Carsaig 
  of 
  a 
  bed, 
  mainly 
  composed 
  of 
  chalk 
  flints, 
  which 
  

   is 
  interposed 
  between 
  the 
  sheets 
  of 
  basaltic 
  lava 
  and 
  attains 
  in 
  some 
  

   places 
  a 
  thickness 
  of 
  25 
  feet. 
  A 
  careful 
  examination 
  of 
  this 
  very 
  

   interesting 
  deposit 
  convinces 
  me 
  that 
  we 
  have 
  here 
  preserved 
  por- 
  

   tions 
  of 
  an 
  old 
  river 
  -gravel, 
  formed 
  by 
  a 
  stream 
  which 
  flowed 
  over 
  

   the 
  surface 
  of 
  the 
  land, 
  in 
  the 
  interval 
  between 
  the 
  outflow 
  of 
  the 
  

   two 
  lava 
  streams 
  which 
  enclose 
  it. 
  The 
  gravels 
  are 
  composed 
  of 
  

   flint 
  detritus 
  of 
  every 
  degree 
  of 
  fineness, 
  mingled 
  with 
  rounded 
  

   fragments 
  of 
  the 
  local 
  hard 
  chalk 
  and 
  of 
  the 
  basaltic 
  lavas 
  of 
  the 
  

   district 
  ; 
  the 
  deposit, 
  which 
  thins 
  out 
  rapidly 
  both 
  eastward 
  and 
  

   westward, 
  exhibits 
  the 
  alternations 
  of 
  beds 
  of 
  coarse 
  and 
  fine-grained 
  

   materials, 
  with 
  occasional 
  seams 
  of 
  sand 
  and 
  loam, 
  the 
  whole 
  being 
  

   marked 
  by 
  much 
  false-bedding 
  ; 
  indeed, 
  so 
  far 
  as 
  it 
  is 
  exposed 
  in 
  

   the 
  sections, 
  this 
  interesting 
  mass 
  of 
  gravels, 
  included 
  between 
  the 
  

   Tertiary 
  basalts, 
  is 
  perfectly 
  similar 
  in 
  every 
  respect 
  to 
  the 
  

   familiar 
  gravels 
  of 
  existing 
  rivers. 
  It 
  is 
  evident 
  that 
  the 
  stream 
  

   which 
  formed 
  these 
  gravels 
  must, 
  in 
  the 
  higher 
  part 
  of 
  its 
  course, 
  

   have 
  flowed 
  through 
  a 
  valley 
  cut 
  in 
  the 
  chalk 
  strata. 
  I 
  have 
  found 
  

   in 
  other 
  cases 
  masses 
  of 
  gravel 
  formed 
  wholly 
  of 
  pebbles 
  of 
  the 
  

   different 
  igneous 
  rocks, 
  which 
  have 
  all 
  the 
  appearance 
  of 
  having 
  

   been 
  formed 
  by 
  streams 
  cutting 
  valleys 
  in 
  the 
  older 
  lavas 
  and 
  

   covered 
  up 
  by 
  subsequent 
  outbursts 
  ; 
  but 
  these 
  of 
  course 
  exhibit 
  

   much 
  less 
  striking 
  characters 
  than 
  the 
  deposit 
  of 
  the 
  Innimore 
  

   of 
  Carsaig. 
  

  

  (5) 
  At 
  very 
  numerous 
  points, 
  both 
  in 
  the 
  North 
  of 
  Ireland 
  and 
  

   in 
  the 
  "Western 
  Isles 
  of 
  Scotland, 
  we 
  find 
  deposits 
  of 
  pisolitic 
  iron- 
  

   ore 
  interbedded 
  with 
  the 
  basalts. 
  That 
  the 
  materials 
  of 
  these 
  

   ferruginous 
  masses 
  were 
  derived 
  from 
  the 
  basaltic 
  rocks 
  on 
  which 
  

   thej* 
  rest 
  there 
  can 
  be 
  no 
  doubt. 
  The 
  actual 
  agency 
  which 
  effected 
  

   the 
  concentration 
  of 
  the 
  iron 
  appears 
  to 
  have 
  been 
  that 
  indicated 
  

   by 
  Mr. 
  David 
  Forbes 
  *, 
  namely 
  the 
  multiplication 
  of 
  organisms 
  of 
  

   a 
  similar 
  kind 
  to 
  those 
  which 
  have 
  formed 
  the 
  well-known 
  " 
  lake- 
  

   ores 
  " 
  of 
  Sweden 
  in 
  recent 
  times. 
  This 
  view 
  is 
  confirmed 
  by 
  the 
  

   occurrence, 
  in 
  association 
  with 
  some 
  of 
  the 
  beds 
  of 
  pisolitic 
  ore, 
  of 
  

   masses 
  of 
  stratified 
  ash, 
  sand, 
  conglomerate, 
  &c, 
  sometimes 
  con- 
  

   taining 
  numerous 
  plant-remains, 
  which 
  are 
  evidently 
  of 
  lacustrine 
  

   origin. 
  Such 
  are 
  the 
  deposits 
  of 
  Ballypalidy 
  in 
  Antrim, 
  at 
  which 
  

  

  suggested 
  by 
  His 
  Grace, 
  that 
  they 
  were 
  entangled 
  in 
  a 
  mud-stream. 
  The 
  dis- 
  

   coloration 
  of 
  the 
  chalk-flints, 
  supposed 
  to 
  be 
  due 
  to 
  the 
  active 
  heat, 
  I 
  regard 
  as 
  

   being 
  the 
  result 
  rather 
  of 
  weathering 
  operations. 
  At 
  Sornrna 
  and 
  Bagno 
  Secco 
  

   in 
  the 
  island 
  of 
  Lipari 
  we 
  find 
  stratified 
  volcanic 
  tuffs 
  with 
  leaves 
  and 
  other 
  

   plant-remains, 
  which 
  present 
  a 
  very 
  striking 
  resemblance 
  to 
  those 
  of 
  Ardtun, 
  

   Ballypalidy, 
  &c. 
  

  

  * 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  sxvi. 
  (1870), 
  pp. 
  164, 
  165. 
  

   Q.J. 
  G. 
  S. 
  No. 
  119. 
  s 
  

  

  