﻿d»b 
  EEV. 
  E. 
  HILL 
  ON 
  THE 
  EOCKS 
  OF 
  

  

  the 
  Alderney 
  grits 
  ; 
  the 
  external 
  differences, 
  however, 
  are 
  great. 
  

   M. 
  Noury, 
  in 
  his 
  excellent 
  monograph 
  on 
  Jersey, 
  regards 
  them 
  as 
  

   Post-Permian 
  on 
  the 
  ground 
  of 
  their 
  relations 
  with 
  the 
  rhyolites. 
  

   MM. 
  Yasseur 
  and 
  Carez, 
  in 
  their 
  map, 
  give 
  them 
  the 
  tint 
  and 
  letter 
  

   of 
  the 
  " 
  Conglomerat 
  Pourpre." 
  The 
  existence 
  of 
  the 
  Alderney 
  beds 
  

   shows 
  at 
  any 
  rate 
  that 
  various 
  conglomerates 
  were 
  being 
  formed 
  

   about 
  that 
  epoch, 
  and 
  the 
  next 
  paragraph 
  will 
  show 
  that 
  the 
  rhyo- 
  

   lites 
  afford 
  no 
  contradictory 
  indications. 
  

  

  This 
  singular 
  and 
  almost 
  unique 
  group 
  of 
  rocks 
  (described 
  under 
  

   the 
  name 
  of 
  rhyolites 
  by 
  Mr. 
  Thos. 
  Davies), 
  which 
  occupies 
  so 
  

   large 
  an 
  area 
  in 
  the 
  eastern 
  part 
  of 
  Jersey, 
  is 
  conjectured 
  by 
  

   M. 
  JNToury 
  to 
  possess 
  a 
  Permian 
  date 
  (Geologie 
  de 
  Jersey, 
  p. 
  129), 
  on 
  

   account, 
  apparently, 
  of 
  its 
  resemblance 
  to 
  certain 
  rocks 
  from 
  the 
  

   Yosges 
  (p. 
  30). 
  But 
  the 
  presence 
  of 
  pebbles 
  which 
  proceeded 
  from 
  

   this 
  group 
  in 
  the 
  grits 
  of 
  Alderney 
  and 
  Omonville, 
  as 
  described 
  

   above, 
  is 
  alone 
  sufficient 
  to 
  show 
  that 
  the 
  group 
  cannot 
  be 
  placed 
  

   later 
  than 
  Cambrian 
  times. 
  

  

  The 
  Jersey 
  conglomerate-pebbles 
  consist 
  chiefly 
  of 
  sedimentary 
  

   rocks 
  which 
  closely 
  resemble 
  the 
  schists 
  of 
  St. 
  Lo, 
  as 
  seen 
  on 
  the 
  

   mainland 
  opposite 
  and 
  elsewhere. 
  The 
  Alderney 
  grits 
  contain 
  sedi- 
  

   mentary 
  pebbles 
  which 
  may 
  well 
  belong 
  to 
  the 
  same 
  formation. 
  If 
  

   either 
  this 
  identity, 
  or 
  the 
  equivalence 
  of 
  the 
  Jersey 
  beds 
  with 
  those 
  

   of 
  Alderney, 
  should 
  hereafter 
  be 
  proved, 
  then, 
  considering 
  the 
  time 
  

   required 
  to 
  harden 
  such 
  beds 
  and 
  wear 
  their 
  fragments 
  into 
  pebbles, 
  

   we 
  should 
  obtain 
  additional 
  evidence 
  of 
  the 
  Pre-Cambrian 
  age 
  of 
  

   the 
  schists 
  of 
  St. 
  Lo. 
  

  

  At 
  different 
  parts 
  of 
  the 
  coast 
  of 
  Jersey 
  there 
  occurs, 
  in 
  con- 
  

   siderable 
  quantity, 
  a 
  diorite. 
  It 
  is 
  in 
  contact 
  with 
  various 
  other 
  

   rocks 
  and 
  is 
  intruded 
  into 
  by 
  several, 
  itself 
  intruding 
  into 
  none. 
  

   There 
  cannot 
  be 
  reasonable 
  doubt 
  that 
  it 
  is 
  anterior 
  to 
  the 
  porphy- 
  

   rites. 
  It 
  is 
  not 
  seen 
  to 
  intrude 
  into 
  the 
  neighbouring 
  argillites 
  of 
  

   St. 
  Aubin's 
  Bay, 
  which 
  are 
  certainly 
  not 
  later 
  than 
  the 
  porphyrite 
  

   group, 
  and 
  which 
  M. 
  Noury 
  correlates 
  with 
  the 
  Granville 
  schists 
  of 
  

   St. 
  Lo. 
  This 
  diorite, 
  then, 
  must 
  be 
  Pre-Cambrian. 
  But 
  both 
  in 
  

   general 
  appearance 
  and 
  in 
  occasional 
  peculiarities 
  it 
  is 
  identical 
  

   with 
  the 
  diorites 
  of 
  Guernsey, 
  and 
  affords 
  evidence 
  that 
  these 
  are 
  

   Pre-Cambrian 
  too. 
  Comparing 
  these 
  again 
  with 
  the 
  hornblendic 
  

   granite 
  of 
  Alderney, 
  overlain 
  unconformably 
  by 
  Upper 
  Cambrian 
  

   grits 
  in 
  which 
  are 
  pebbles 
  of 
  dykes 
  found 
  in 
  the 
  granites, 
  and 
  con- 
  

   sidering 
  also 
  the 
  kindred 
  granites 
  of 
  Sark, 
  Herm, 
  and 
  Jethou, 
  we 
  

   must 
  recognize 
  the 
  existence 
  over 
  a 
  great 
  area 
  of 
  Pre-Cambrian 
  

   coarsely 
  crystalline 
  igneous 
  rock. 
  

  

  The 
  granites 
  throughout 
  this 
  area 
  show 
  results 
  of 
  earth-move- 
  

   ments 
  to 
  a 
  certain 
  extent 
  ; 
  they 
  bear 
  variable 
  traces 
  of 
  crushing, 
  as 
  

   has 
  been 
  previously 
  mentioned- 
  This 
  amount 
  is 
  not 
  very 
  great, 
  

   perhaps 
  not 
  more 
  than 
  that 
  to 
  which 
  even 
  the 
  grits 
  have 
  been 
  sub- 
  

   jected. 
  But 
  the 
  so-called 
  " 
  Protogine 
  " 
  or 
  gneiss 
  of 
  the 
  Cap 
  La 
  

   Hague 
  region 
  has 
  undergone 
  a 
  tremendous 
  crush, 
  and 
  has 
  been 
  

   reduced 
  to 
  a 
  grey 
  gneiss 
  with 
  foliation 
  N.E. 
  to 
  S/W. 
  The 
  singular 
  

   syenite 
  of 
  Coutances 
  has 
  a 
  strong 
  cleavage 
  IN", 
  to 
  S. 
  or 
  K".1S".E. 
  to 
  

  

  