﻿1864. 
  j 
  WLtfTLE 
  — 
  HOBAKT. 
  4G9 
  

  

  to 
  be 
  unfossiliferous. 
  About 
  a 
  quarter 
  of 
  a 
  mile 
  higher 
  up 
  we 
  meet 
  

   with 
  the 
  uppermost 
  members 
  of 
  the 
  Silurian 
  system. 
  

  

  5. 
  Silurian 
  System 
  (?). 
  — 
  The 
  Silurian 
  strata 
  consist 
  of 
  a 
  dark- 
  

   coloured 
  inferior 
  slate, 
  in 
  which, 
  as 
  yet, 
  no 
  fossils 
  have 
  been 
  found. 
  

   This 
  slate 
  rests 
  upon 
  a 
  thin 
  bedding 
  of 
  tilestone, 
  and 
  this 
  again 
  

   reposes 
  upon 
  mica-schist, 
  and 
  from 
  this 
  point 
  to 
  the 
  basaltic 
  columns 
  

   of 
  the 
  mountain 
  all 
  is 
  a 
  terra 
  incognita. 
  

  

  Mr. 
  Gould 
  has 
  lately 
  shown 
  me 
  a 
  Cahjmene 
  Blumenoacliii 
  which 
  

   he 
  obtained 
  from 
  the 
  Silurian 
  slate 
  of 
  the 
  interior, 
  correspond- 
  

   ing 
  to 
  that 
  above 
  mentioned, 
  and 
  therefore 
  I 
  have 
  reason 
  to 
  

   hope 
  that 
  I 
  may 
  yet 
  find 
  the 
  Mount 
  Wellington 
  slates 
  fossiliferous. 
  

   The 
  strike 
  of 
  these 
  beds 
  is 
  nearly 
  due 
  north 
  and 
  south, 
  with 
  a 
  dip 
  

   of 
  about 
  43° 
  east. 
  They 
  are 
  again 
  forced 
  up 
  by 
  the 
  greenstone 
  

   which 
  rests 
  upon 
  them 
  on 
  the 
  Huon 
  Track, 
  and 
  dipping 
  again 
  very 
  

   precipitously 
  are 
  then 
  entirely 
  lost 
  sight 
  of. 
  The 
  Silurian 
  system 
  

   appears 
  to 
  be 
  very 
  feebly 
  developed 
  in 
  Tasmania, 
  according 
  to 
  the 
  

   reports 
  of 
  Mr. 
  Gould. 
  

  

  6. 
  Boulder 
  Drift 
  (?) 
  and 
  Post-Pliocene 
  Deposits. 
  — 
  There 
  is 
  one 
  

   other 
  very 
  interesting 
  formation 
  in 
  this 
  city, 
  which 
  for 
  want 
  

   of 
  a 
  better 
  name 
  I 
  will 
  call 
  the 
  Boulder 
  Drift, 
  although 
  in 
  

   many 
  respects 
  it 
  differs 
  from 
  the 
  formation 
  of 
  the 
  same 
  name 
  in 
  

   Great 
  Britain. 
  This 
  consists 
  of 
  immense 
  boulders, 
  principally 
  of 
  

   felspathic 
  trap 
  and 
  greenstone 
  ; 
  imbedded 
  in 
  stiff 
  clay 
  in 
  some 
  parts, 
  

   and 
  in 
  others 
  in 
  loam. 
  In 
  many 
  instances 
  these 
  boulders 
  are 
  

   associated 
  with 
  fragments 
  of 
  New 
  Red 
  Sandstone 
  and 
  nodular 
  masses 
  

   of 
  dolomite. 
  At 
  other 
  times 
  we 
  find 
  the 
  boulders, 
  which 
  very 
  

   frequently 
  are 
  globiform, 
  with 
  exfoliating 
  surfaces 
  where 
  exposed 
  to 
  

   the 
  air, 
  cemented 
  together 
  by 
  oxide 
  of 
  iron, 
  which 
  appears 
  to 
  

   enter 
  largely 
  into 
  their 
  composition 
  ; 
  and 
  in 
  many 
  places 
  there 
  are 
  

   veins 
  of 
  a 
  mineral 
  with 
  needle-shaped 
  crystals 
  distributed 
  among 
  

   the 
  boulders*. 
  This 
  mineral 
  I 
  am 
  inclined 
  to 
  think 
  is 
  a 
  kind 
  of 
  

   sulphate 
  of 
  lime. 
  However, 
  it 
  appears 
  to 
  rapidly 
  deliquesce 
  upon 
  

   exposure 
  to 
  the 
  air 
  into 
  a 
  marl. 
  In 
  some 
  places 
  this 
  formation 
  

   constitutes 
  hills 
  of 
  considerable 
  size, 
  some 
  of 
  which 
  have 
  been 
  

   worked 
  for 
  the 
  nodules 
  of 
  dolomite 
  they 
  contain. 
  

  

  The 
  next, 
  and 
  last, 
  important 
  feature 
  in 
  the 
  geology 
  of 
  Hobart 
  to 
  

   which 
  I 
  must 
  briefly 
  refer, 
  is 
  that 
  of 
  the 
  Post-Tertiary 
  marine 
  de- 
  

   posits 
  (?). 
  In 
  a 
  paper 
  which 
  I 
  read 
  before 
  the 
  Tasmanian 
  Royal 
  

   Society 
  a 
  few 
  weeks 
  since, 
  I 
  pointed 
  out 
  that, 
  until 
  a 
  very 
  recent 
  

   period 
  in 
  the 
  geological 
  annals 
  of 
  this 
  island, 
  a 
  great 
  portion 
  of 
  what 
  

   now 
  constitutes 
  the 
  site 
  of 
  this 
  city 
  had 
  been 
  under 
  water. 
  This 
  is 
  

   proved 
  by 
  the 
  extensive 
  deposits 
  of 
  comminuted 
  Shells, 
  all 
  of 
  recent 
  

   species, 
  which 
  are 
  met 
  with, 
  for 
  miles, 
  indeed, 
  along 
  the 
  banks 
  

   of 
  the 
  Derwent. 
  Some 
  of 
  these 
  deposits 
  are 
  at 
  an 
  elevation 
  of 
  

   upwards 
  of 
  one 
  hundred 
  feet 
  above 
  high-water 
  mark, 
  and 
  from 
  fifty 
  

   to 
  one 
  hundred 
  yards 
  from 
  the 
  water's 
  edge, 
  plainly 
  showing 
  thereby 
  

   that 
  a 
  very 
  recent 
  elevation 
  of 
  the 
  land 
  has 
  taken 
  place. 
  Judging 
  

   from 
  the 
  condition 
  of 
  the 
  Shells, 
  I 
  think 
  this 
  formation 
  may 
  be 
  as- 
  

   signed 
  to 
  the 
  Post-pliocene 
  period. 
  

  

  * 
  See 
  specimen 
  No. 
  7, 
  Coll. 
  Geol. 
  Soc. 
  

  

  