﻿280 
  J. 
  S. 
  GARDNER 
  ON 
  THE 
  GEOLOGY 
  OE 
  MADEIRA. 
  

  

  extinct 
  forms, 
  and 
  several 
  to 
  plants 
  not 
  now 
  indigenous 
  to 
  the 
  island, 
  

   a 
  series 
  of 
  mistakes 
  subsequently 
  pointed 
  out 
  and 
  rectified 
  by 
  Lowe 
  

   in 
  the 
  ' 
  Botany 
  of 
  Madeira.' 
  

  

  This 
  appears 
  to 
  be 
  the 
  only 
  known 
  lignitic 
  formation 
  in 
  the 
  island, 
  

   and 
  is 
  the 
  only 
  locality 
  whence 
  fossil 
  plants 
  have 
  been 
  obtained, 
  

   except 
  that 
  discovered 
  by 
  Mr. 
  Yate 
  Johnson, 
  and 
  now 
  to 
  be 
  described. 
  

  

  Facing 
  the 
  Ilha 
  do 
  Porto 
  da 
  Cruz, 
  just 
  east 
  of 
  and 
  overshadowed 
  

   by 
  the 
  vast 
  Penha 
  d'Aguia, 
  whose 
  sea-front 
  presents 
  a 
  vertical 
  cliff 
  

   1700 
  feet 
  in 
  height, 
  lies 
  a 
  small 
  promontory, 
  whose 
  height, 
  though 
  

   some 
  150 
  feet, 
  is 
  rendered 
  utterly 
  insignificant 
  by 
  the 
  proximity 
  of 
  

   its 
  gigantic 
  neighbour. 
  It 
  is 
  capped 
  with 
  a 
  whitish 
  or 
  ashy-grey 
  

   trachytic 
  tuff, 
  succeeded 
  by 
  layers 
  of 
  hard 
  breccia 
  and 
  brittle, 
  ferru- 
  

   ginous, 
  sandy 
  tuff, 
  about 
  15 
  beds 
  of 
  which 
  recur 
  interstratificd 
  together. 
  

   In 
  one 
  of 
  the 
  lowest 
  beds 
  of 
  the 
  latter 
  I 
  obtained 
  beautifully 
  preserved 
  

   leaves 
  of 
  two 
  species 
  of 
  bramble, 
  and 
  both 
  the 
  leaves 
  and 
  flower-spikes 
  

   of 
  a 
  Carex, 
  while 
  a 
  little 
  to 
  the 
  west 
  a 
  few 
  silicified 
  stems 
  were 
  im- 
  

   bedded. 
  The 
  leaf-bed 
  I 
  saw 
  was 
  extremely 
  local, 
  and 
  may 
  not 
  have 
  

   been 
  exactly 
  the 
  same 
  as 
  that 
  observed 
  in 
  the 
  same 
  locality 
  by 
  Mr. 
  

   Yate 
  Johnson 
  some 
  years 
  since, 
  who, 
  indeed, 
  found 
  leaves 
  on 
  different 
  

   horizons, 
  some 
  of 
  which 
  cannot 
  be 
  referred 
  to 
  Bubus. 
  The 
  whole 
  

   formation 
  rests 
  upon 
  a 
  platform 
  of 
  highly 
  vesicular 
  basaltic 
  lava, 
  under- 
  

   mined 
  into 
  deep 
  caverns 
  by 
  the 
  sea. 
  These 
  tuffs 
  and 
  those 
  overlying 
  

   the 
  formation 
  are 
  the 
  only 
  deposits 
  of 
  the 
  kind 
  in 
  the 
  island 
  ; 
  they 
  

   belong 
  to 
  the 
  very 
  latest 
  of 
  the 
  igneous 
  series 
  of 
  Madeira, 
  and 
  arc 
  

   probably 
  Quaternary 
  or 
  Recent. 
  Pilling 
  up 
  a 
  valley 
  as 
  they 
  do, 
  

   they 
  must 
  have 
  been 
  formed 
  after 
  the 
  erosion 
  of 
  the 
  whole 
  series 
  of 
  

   basalts 
  of 
  the 
  Penha 
  d'Aguia 
  into 
  the 
  present 
  rectangular 
  mass, 
  

   2000 
  feet 
  high, 
  by 
  torrents 
  whose 
  powers 
  seem 
  utterly 
  inadequate 
  

   to 
  have 
  accomplished 
  the 
  work. 
  Beds 
  of 
  lava 
  and 
  ash 
  with 
  an 
  

   aggregate 
  thickness 
  of 
  at 
  least 
  2000 
  feet 
  must 
  have 
  been 
  ejected, 
  at 
  

   intervals 
  which 
  permitted 
  the 
  formation 
  of 
  considerable 
  accumulations 
  

   of 
  vegotable 
  soil, 
  and 
  again 
  eroded 
  through 
  to 
  the 
  sea-level, 
  between 
  

   the 
  close 
  of 
  the 
  Miocene 
  and 
  the 
  closo 
  of 
  the 
  volcanic 
  period, 
  if 
  closed 
  

   it 
  be, 
  of 
  Madeira. 
  

  

  In 
  conclusion 
  I 
  have 
  to 
  express 
  my 
  deep 
  obligations 
  to 
  Mr. 
  Leland 
  

   C. 
  Cossart 
  for 
  the 
  hospitality 
  which 
  enabled 
  me 
  to 
  explore 
  so 
  much 
  of 
  

   Madeira, 
  and 
  to 
  Mr. 
  Charles 
  Cossart 
  for 
  the 
  companionship 
  which 
  

   rendered 
  our 
  many 
  fatiguing 
  excursions 
  a 
  pleasure, 
  as 
  well 
  as 
  for 
  the 
  

   valuable 
  assistance 
  rendered 
  me 
  in 
  collecting 
  specimens 
  and 
  

   arranging 
  for 
  their 
  safe 
  arrival 
  at 
  their 
  destination. 
  

  

  Discussion. 
  

  

  Mr. 
  Etheridge 
  said 
  that 
  the 
  coralline 
  limestone 
  appeared 
  to 
  him 
  to 
  

   belong 
  to 
  the 
  same 
  as 
  that 
  of 
  St. 
  Thomas's, 
  Barbadoes, 
  and 
  other 
  

   West-Indian 
  localities. 
  He 
  asked 
  if 
  the 
  author 
  had 
  seen 
  the 
  Phola- 
  

   domya 
  mentioned 
  ; 
  of 
  that 
  genus 
  only 
  one 
  species 
  now 
  existed, 
  

   namely 
  P. 
  Candida. 
  As 
  for 
  the 
  leaves, 
  a 
  most 
  able 
  botanist 
  was 
  

   present. 
  Much 
  information 
  upon 
  the 
  Miocene 
  rocks 
  may 
  be 
  obtained 
  

  

  