﻿603 
  Transactions, 
  — 
  Geology, 
  

  

  64 
  lava- 
  streams 
  formed 
  of 
  a 
  scoriaceous 
  basaltic 
  and 
  doleritic 
  lava, 
  

   some 
  of 
  them 
  changing 
  so 
  gradually 
  into 
  agglomeratic 
  beds 
  

   that 
  the 
  line 
  between 
  them 
  cannot 
  be 
  clearly 
  defined, 
  

   39 
  beds 
  of 
  agglomerates, 
  a 
  few 
  of 
  them 
  changing 
  into 
  scoriaceous 
  

   lava, 
  but 
  most 
  of 
  them 
  consisting 
  of 
  scorise, 
  lapilli, 
  and 
  other 
  

   ejecta, 
  imbedded 
  in 
  ashes, 
  A 
  few 
  of 
  them 
  have 
  a 
  brecciated 
  

   appearance. 
  

   19 
  beds 
  of 
  laterite, 
  clays, 
  and 
  slope 
  deposits, 
  partly 
  or 
  wholly 
  burnt 
  

  

  by 
  overlying 
  lava-streams, 
  and 
  

   1 
  small 
  layer 
  of 
  bolus 
  — 
  together 
  174. 
  

   These 
  beds 
  are 
  intersected 
  by 
  32 
  dykes, 
  18 
  consisting 
  of 
  trachyte 
  lava 
  

   (of 
  which 
  five 
  do 
  not 
  reach 
  to 
  the 
  roof 
  of 
  the 
  tunnel), 
  and 
  14 
  of 
  a 
  basic 
  

   nature 
  (five 
  of 
  them 
  being 
  intermediate 
  in 
  character, 
  trachy-dolerites). 
  One 
  

   of 
  them 
  comes 
  from 
  the 
  top 
  of 
  the 
  tunnel. 
  

  

  Beginning 
  at 
  the 
  southern 
  or 
  Lyttelton 
  side 
  of 
  the 
  tunnel, 
  w^e 
  observe 
  

   that 
  a 
  large 
  bed 
  of 
  loam 
  has 
  been 
  deposited 
  upon 
  the 
  volcanic 
  rocks, 
  being 
  

   thickest 
  on 
  the 
  lowest 
  third 
  of 
  the 
  caldera 
  wall. 
  This 
  peculiar 
  rock, 
  which, 
  

   when 
  in 
  small 
  pieces, 
  is 
  easily 
  pulverized 
  between 
  the 
  fingers, 
  has 
  a 
  re- 
  

   markable 
  consistency 
  and 
  solidity 
  when 
  in 
  large 
  masses, 
  and 
  is 
  of 
  sub- 
  

   aerial 
  origin. 
  It 
  may 
  be 
  designated 
  as 
  loess, 
  an 
  expression 
  now 
  extensively 
  

   used 
  in 
  Europe 
  for 
  similar 
  deposits. 
  It 
  owes 
  its 
  origin 
  to 
  various 
  processes, 
  

   of 
  which 
  rain, 
  wind, 
  and 
  vegetation 
  are 
  the 
  principal 
  factors. 
  This 
  bed 
  of 
  

   loess, 
  which 
  in 
  some 
  localities 
  is 
  more 
  than 
  100 
  feet 
  thick, 
  changes 
  

   gradually 
  before 
  we 
  reach 
  the 
  volcanic 
  rock 
  to 
  a 
  true 
  slope 
  deposit, 
  

   consisting 
  of 
  fragments 
  of 
  rock 
  more 
  or 
  less 
  rounded, 
  the 
  lines 
  of 
  junction 
  

   being 
  often 
  impossible 
  to 
  trace, 
  owing 
  to 
  the 
  decomposition 
  of 
  the 
  volcanic 
  

   rocks 
  immediately 
  below 
  the 
  slope 
  deposits. 
  The 
  greatest 
  amount 
  of 
  

   agglomerate, 
  consisting 
  of 
  scorite, 
  lapilli, 
  and 
  ashes 
  is, 
  as 
  might 
  be 
  ex- 
  

   pected, 
  congregated 
  on 
  the 
  inner 
  side 
  of 
  the 
  caldera 
  wall, 
  not 
  far 
  from 
  the 
  

   focus 
  of 
  eruption. 
  These 
  more 
  or 
  less 
  incoherent 
  beds, 
  of 
  which 
  each 
  was 
  

   probably 
  formed 
  during 
  one 
  eruption, 
  have 
  generally 
  an 
  inward 
  as 
  well 
  as 
  

   an 
  outward 
  dip, 
  of 
  which 
  the 
  beds 
  232 
  to 
  241 
  close 
  to 
  the 
  entrance 
  of 
  the 
  

   tunnel 
  at 
  Lyttelton 
  form 
  a 
  notable 
  instance. 
  They 
  were 
  without 
  doubt 
  

   deposited 
  on 
  the 
  lip 
  of 
  the 
  crater. 
  Near 
  the 
  Lyttelton 
  end 
  they 
  are 
  much 
  

   disturbed. 
  Two 
  stony 
  lava-streams 
  cross 
  these 
  agglomerate 
  beds, 
  and 
  we 
  

   have 
  to 
  assume 
  that 
  after 
  No. 
  231 
  was 
  formed, 
  the 
  lava-stream 
  233, 
  

   ascending 
  from 
  the 
  mouth 
  of 
  the 
  crater, 
  had 
  consolidated 
  over 
  it, 
  being 
  in 
  

   its 
  turn 
  covered 
  by 
  a 
  new 
  talus 
  of 
  ejecta 
  sloping 
  inwards 
  to 
  the 
  crater's 
  

   mouth. 
  After 
  these 
  latter 
  beds 
  234 
  and 
  234a, 
  were 
  formed, 
  a 
  new 
  stony 
  

   lava-stream, 
  No. 
  237, 
  ascended, 
  in 
  which 
  case 
  Nos. 
  231, 
  234, 
  and 
  238 
  to 
  

   241 
  were 
  three 
  distinct 
  agglomerate 
  beds, 
  covered 
  and 
  preserved 
  on 
  their 
  

  

  