﻿30 
  GEOLOGICAL 
  MEMOIES. 
  

  

  attains 
  a 
  much 
  greater 
  thickness, 
  being 
  from 
  100 
  to 
  150 
  feet. 
  It 
  

   consists 
  here 
  principally 
  of 
  a 
  series 
  of 
  sandstones 
  and 
  clays, 
  together 
  

   with 
  the 
  breccia 
  of 
  the 
  bone-bed. 
  

  

  Still 
  greater 
  interest 
  is 
  attached 
  to 
  the 
  diversity 
  in 
  the 
  fauna 
  and 
  

   flora 
  in 
  the 
  various 
  localities 
  than 
  to 
  the 
  lithological 
  differences. 
  As 
  

   the 
  bone-bed 
  is 
  almost 
  confined 
  to 
  Wiirtemberg, 
  Northern 
  Germany, 
  

   and 
  England, 
  so 
  also 
  we 
  find 
  other 
  forms 
  of 
  organic 
  remains 
  restricted 
  

   to 
  particular 
  regions. 
  The 
  large 
  GerviUia 
  hrflata 
  is 
  only 
  met 
  with 
  in 
  

   the 
  Alps, 
  as 
  also 
  are 
  the 
  different 
  Corals 
  (LitJiodendron, 
  Thamnastrea, 
  

   &c), 
  and 
  the 
  various 
  Brachiopods, 
  Cephalopods, 
  and 
  Echinoderms. 
  

   Plants, 
  beautifully 
  preserved, 
  form 
  large 
  deposits 
  in 
  Sweden 
  and 
  

   Eranconia. 
  In 
  Northern 
  and 
  Central 
  Germany 
  the 
  sandstones 
  of 
  the 
  

   Contorta-zone 
  are 
  full 
  of 
  Equisetum 
  and 
  Cycads 
  ; 
  and 
  in 
  Wiirtemberg 
  

   and 
  Luxemburg, 
  traces 
  of 
  such 
  Plants 
  occur 
  in 
  the 
  form 
  of 
  small 
  car- 
  

   bonaceous 
  layers 
  and 
  particles. 
  In 
  England, 
  and 
  in 
  the 
  Erench 
  

   Arkose, 
  no 
  traces 
  of 
  Plants 
  are 
  met 
  with, 
  except 
  certain 
  undistin- 
  

   guishable 
  Eucoid 
  remains. 
  

  

  But 
  few 
  forms 
  are 
  of 
  universal 
  occurrence, 
  notwithstanding 
  the 
  

   considerable 
  number 
  of 
  species. 
  The 
  following 
  are 
  the 
  leading 
  forms 
  

   of 
  the 
  Contorta-zone, 
  though 
  one 
  or 
  other 
  of 
  these 
  may 
  be 
  wanting 
  

   in 
  certain 
  localities. 
  

  

  Avicula 
  contorta. 
  Schizodus 
  prsecursor. 
  

  

  Grervillia 
  prsecursor. 
  Pecten 
  acutiauritus 
  (Yaloniensis.) 
  

  

  Cardium 
  Pkseticuui. 
  Lima 
  prsecursor. 
  

  

  Mytilus 
  minutus. 
  Leda 
  percaudata. 
  

  

  Anatina 
  prsecursor. 
  Sargodon 
  Tomicus. 
  

  

  Anatina 
  Suessi. 
  Acrodus 
  minimus. 
  

  

  The 
  author 
  next 
  considers 
  the 
  geological 
  position 
  of 
  the 
  Contorta- 
  

   zone, 
  and 
  the 
  vexed 
  question 
  as 
  to 
  whether 
  it 
  should 
  be 
  regarded 
  

   as 
  belonging 
  to 
  the 
  Keuper 
  or 
  the 
  Lias. 
  All 
  attempts 
  to 
  obtain 
  

   decided 
  distinguishing 
  characters, 
  whether 
  palasontological, 
  litholo- 
  

   gical, 
  or 
  stratigraphical, 
  have 
  hitherto 
  been 
  unsuccessful, 
  and 
  the 
  

   Contorta-zone 
  continues 
  to 
  stand 
  out 
  as 
  a 
  natural 
  passage-bed, 
  

   equally 
  allied 
  to 
  the 
  Lias 
  and 
  to 
  the 
  Keuper. 
  

  

  Lithologically 
  the 
  dark 
  grey 
  sandy 
  and 
  shaly 
  clay 
  of 
  the 
  bone- 
  

   bed 
  is, 
  in 
  England, 
  as 
  closely 
  allied 
  to 
  the 
  variegated 
  marls 
  of 
  the 
  

   Keuper 
  as 
  to 
  the 
  black 
  limestone 
  of 
  the 
  Lias. 
  The 
  Arkose 
  of 
  Central 
  

   France 
  is 
  equally 
  related 
  to 
  both 
  the 
  older 
  and 
  newer 
  beds. 
  The 
  

   hard 
  brown 
  bone-bed 
  sandstone 
  and 
  its 
  associated 
  clays 
  in 
  the 
  east 
  

   of 
  Erance 
  and 
  in 
  Wiirtemberg 
  are 
  closely 
  connected 
  with 
  beds 
  of 
  a 
  

   similar 
  nature 
  in 
  the 
  Keuper, 
  and 
  form 
  a 
  marked 
  contrast 
  to 
  the 
  

   black 
  limestone-bands 
  of 
  the 
  Lower 
  Lias. 
  In 
  the 
  Alps 
  there 
  is 
  an 
  

   equal 
  resemblance, 
  lithologically, 
  to 
  the 
  older 
  and 
  to 
  the 
  newer 
  

   strata. 
  

  

  The 
  stratigraphical 
  bearings 
  of 
  the 
  Contorta-beds 
  indicate 
  rather 
  

   a 
  relationship 
  with 
  the 
  Keuper 
  ; 
  and 
  by 
  alternation 
  they 
  are 
  much 
  

   more 
  closely 
  connected 
  with 
  it 
  than 
  with 
  the 
  Lias 
  ; 
  for 
  the 
  sandstone 
  

   of 
  this 
  zone 
  in 
  extra- 
  alpine 
  regions, 
  as 
  well 
  as 
  in 
  the 
  Erench 
  Arkose, 
  

   alternates 
  with 
  the 
  marls 
  and 
  clays 
  of 
  the 
  Keuper, 
  but 
  never 
  with 
  

   the 
  limestone 
  of 
  the 
  Lias. 
  If 
  we 
  regard 
  the 
  conformability 
  or 
  un- 
  

  

  