﻿CRYSTALLINE 
  EOCKS 
  OF 
  THE 
  ALPS, 
  97 
  

  

  practically 
  absent. 
  In 
  confirmation 
  of 
  this 
  inference 
  I 
  may 
  mention 
  

   that 
  the 
  schists, 
  to 
  which, 
  from 
  their 
  lithological 
  peculiarities, 
  I 
  

   have 
  given 
  the 
  name 
  of 
  the 
  Tremola 
  schists, 
  appear 
  to 
  be 
  rare 
  in 
  the 
  

   Tyrol, 
  in 
  the 
  French 
  and 
  in 
  many 
  parts 
  of 
  the 
  Central 
  Alps, 
  and 
  I 
  

   have 
  not 
  yet 
  seen 
  them 
  so 
  fully 
  developed 
  as 
  on 
  the 
  southern 
  side 
  

   of 
  the 
  St. 
  Gothard. 
  

  

  Lastly, 
  and 
  seemingly 
  lowest, 
  comes 
  the 
  great 
  group 
  of 
  strong 
  

   (banded) 
  gneisses 
  and 
  granitoid 
  gneisses, 
  which, 
  as 
  said 
  above, 
  some- 
  

   times 
  appears 
  to 
  graduate 
  into 
  the 
  last-named. 
  In 
  the 
  present 
  state 
  

   of 
  our 
  knowledge 
  it 
  is 
  often 
  dim 
  cult 
  to 
  identify 
  this 
  group 
  with 
  cer- 
  

   tainty, 
  because 
  we 
  are 
  ignorant 
  of 
  the 
  history 
  of 
  its 
  more 
  granitoid 
  

   members. 
  Nevertheless, 
  we 
  find 
  banded 
  gneisses 
  of 
  a 
  " 
  Laurentian 
  '? 
  

   aspect 
  in 
  the 
  French 
  Alps 
  and 
  the 
  Central 
  Tyrol, 
  and 
  in 
  some 
  parts 
  

   of 
  Switzerland 
  ; 
  and 
  even 
  if 
  the 
  granitoid 
  members 
  — 
  such 
  as 
  the 
  

   great 
  massif 
  'of 
  the 
  Central 
  Oberland 
  — 
  are 
  (as 
  I 
  believe 
  them 
  to 
  be 
  in 
  

   many 
  cases) 
  granites 
  subsequently 
  modified, 
  and 
  so 
  igneous 
  in 
  origin, 
  

   these 
  are 
  curiously 
  like 
  the 
  granitoid 
  rocks 
  which 
  elsewhere 
  are 
  

   grouped 
  with 
  Laurentian 
  and 
  Hebridean 
  rocks, 
  and 
  are 
  unlike 
  the 
  

   granitoid 
  rocks 
  which 
  in 
  other 
  parts 
  of 
  the 
  Alps 
  are 
  associated 
  with 
  

   the 
  above-mentioned 
  groups. 
  This, 
  to 
  say 
  the 
  least, 
  is 
  a 
  remarkable 
  

   coincidence. 
  

  

  The 
  result, 
  then, 
  of 
  my 
  examination 
  has 
  been 
  to 
  confirm 
  the 
  view, 
  

   expressed 
  in 
  my 
  Address, 
  that, 
  broadly 
  speaking, 
  a 
  stratigraphical 
  

   succession 
  can 
  be 
  detected 
  in 
  the 
  gneisses 
  and 
  schists 
  of 
  the 
  Alps, 
  

   and 
  that 
  these 
  rocks 
  are 
  of 
  Archaean 
  age. 
  There 
  have 
  also 
  been 
  

   some 
  negative 
  results. 
  It 
  has 
  been 
  confidently 
  asserted 
  that 
  be- 
  

   tween 
  the 
  second 
  and 
  third 
  groups 
  in 
  the 
  Alps 
  an 
  important 
  one 
  

   should 
  be 
  intercalated, 
  to 
  which 
  the 
  name 
  of 
  Pietra 
  Yerde 
  has 
  been 
  

   given. 
  It 
  has 
  been 
  defined 
  as 
  distinguished 
  by 
  " 
  the 
  frequent 
  pre- 
  

   sence 
  therein 
  of 
  serpentine, 
  diorite, 
  diabase, 
  and 
  related 
  rocks 
  of 
  a 
  

   greenish 
  colour 
  " 
  *. 
  As 
  most 
  of 
  the 
  Alpine 
  serpentines 
  are 
  altered 
  

   peridotites, 
  as 
  diorite 
  and 
  diabase 
  are 
  igneous 
  rocks, 
  it 
  is 
  obviously 
  

   necessary, 
  before 
  taking 
  these 
  as 
  characteristics 
  of 
  a 
  geological 
  group 
  

   of 
  stratigraphical 
  value, 
  to 
  show 
  that 
  they 
  are 
  contemporaneous 
  in 
  

   origin. 
  This, 
  which 
  one 
  would 
  have 
  thought 
  would 
  have 
  appeared 
  

   to 
  any 
  competent 
  petrologist 
  a 
  necessary 
  preliminary, 
  has 
  not 
  been 
  

   done, 
  and, 
  as 
  I 
  know 
  well, 
  it 
  cannot 
  be 
  done. 
  The 
  group 
  is 
  also 
  

   said 
  to 
  contain 
  crystalline 
  limestones, 
  which, 
  however, 
  so 
  far 
  as 
  I 
  

   know, 
  are 
  very 
  local 
  and 
  not 
  readily 
  separable 
  from 
  their 
  associated 
  

   gneisses 
  and 
  schists, 
  so 
  that 
  I 
  have 
  been 
  unable 
  to 
  find 
  any 
  rocks 
  at 
  

   this 
  horizon 
  which 
  can 
  be 
  formed 
  into 
  a 
  definite 
  group. 
  It 
  is, 
  indeed, 
  

   true 
  that 
  hornblendic 
  rocks 
  appear 
  to 
  be 
  rather 
  common 
  just 
  about 
  

   a 
  particular 
  horizon 
  ; 
  but 
  these 
  occur 
  so 
  sporadically 
  that 
  anyone 
  

   who 
  regards 
  them 
  as 
  of 
  stratigraphical 
  value 
  is 
  bound 
  to 
  prove 
  that 
  

   they 
  are 
  not 
  intrusive. 
  Serpentine 
  certainly 
  is 
  of 
  no 
  value 
  as 
  

   marking 
  an 
  horizon 
  in 
  the 
  Alps, 
  for 
  it 
  occurs 
  very 
  commonly 
  in 
  the 
  

   Upper 
  Schist. 
  It 
  has, 
  indeed, 
  been 
  asserted 
  that 
  the 
  serpentines 
  

   are 
  sometimes, 
  both 
  here 
  and 
  in 
  the 
  Apennines, 
  insular 
  masses 
  of 
  

  

  * 
  " 
  Geol. 
  Hist, 
  of 
  Serpentine," 
  Trans. 
  Roy. 
  Soc. 
  Canada, 
  vol. 
  i. 
  p. 
  154. 
  

   Q.J.G. 
  S. 
  No. 
  177. 
  h 
  

  

  