﻿514 
  Scientific 
  Intelligence. 
  

  

  characterized 
  by 
  different 
  kinds 
  of 
  earthquakes. 
  The 
  Alpine 
  

   system 
  is 
  not 
  yet 
  old, 
  fault-formation 
  is 
  still 
  in 
  progress, 
  and 
  the 
  

   fault-slips 
  are 
  long 
  and 
  frequently 
  recurring. 
  In 
  Great 
  Britain, 
  

   we 
  meet 
  with 
  a 
  later 
  stage. 
  Fault-formation 
  in 
  our 
  seismic 
  area 
  

   is 
  more 
  advanced, 
  and 
  slipping 
  takes 
  place 
  so 
  slowly 
  and 
  over 
  

   distances 
  so 
  short, 
  that 
  our 
  earthquakes 
  are 
  rare 
  and 
  the 
  areas 
  

   disturbed 
  by 
  them 
  more 
  or 
  less 
  circular 
  in 
  form. 
  

  

  Every 
  stage 
  in 
  the 
  process, 
  however, 
  requires 
  investigation, 
  

   and 
  that 
  of 
  which 
  our 
  British 
  earthquakes 
  are 
  witness 
  is 
  certainly 
  

   deserving 
  of 
  attentive 
  study. 
  Unattractive 
  though 
  it 
  may 
  be 
  at 
  

   first 
  sight, 
  the 
  epoch 
  immediately 
  preceding 
  the 
  death 
  of 
  a 
  

   mountain-chain, 
  is 
  at 
  least 
  as 
  interesting 
  to 
  the 
  geologist 
  as 
  the 
  

   more 
  vigorous 
  periods 
  of 
  origin 
  and 
  growth.— 
  pp. 
  28, 
  29. 
  

  

  2. 
  On 
  the 
  Formation 
  of 
  Graphite 
  in 
  Gontact-metamorphism. 
  

   ■ 
  — 
  Graphite 
  is 
  found 
  naturally 
  in 
  various 
  Archean 
  rocks. 
  Gen- 
  

   erally 
  it 
  occurs 
  in 
  beds 
  or 
  pockets, 
  in 
  gneiss, 
  mica 
  slate, 
  clay 
  

   slate, 
  granular 
  limestone, 
  etc. 
  ; 
  whence 
  is 
  obtained 
  most 
  of 
  that 
  

   used 
  in 
  the 
  arts. 
  Besides 
  this, 
  a 
  second 
  mode 
  of 
  occurrence 
  of 
  

   graphite, 
  which 
  is 
  of 
  great 
  interest, 
  is 
  that 
  in 
  which 
  in 
  certain 
  

   Archean 
  rocks 
  it 
  replaces 
  either 
  wholly 
  or 
  partially, 
  the 
  mica. 
  

   Graphite-mica-schists 
  are 
  known, 
  and 
  also 
  graphite-gneisses, 
  in 
  

   which 
  the 
  scales 
  of 
  mica 
  in 
  ordinary 
  mica-schists 
  and 
  gneisses 
  

   are 
  partly 
  or 
  wholly 
  replaced 
  by 
  scales 
  of 
  graphite 
  ; 
  and 
  a 
  schis- 
  

   tose 
  rock 
  called 
  graphite-schist 
  exists 
  which 
  consists 
  substantially 
  

   of 
  graphite 
  and 
  quartz. 
  Even 
  more 
  noteworthy 
  is 
  the 
  occur- 
  

   rence 
  of 
  graphite 
  scales 
  in 
  granite, 
  in 
  place 
  of 
  the 
  usual 
  mica 
  

   scales. 
  Beck 
  and 
  Luzi 
  have 
  now 
  observed 
  the 
  occurrence 
  of 
  

   beautifully 
  crystallized 
  graphite 
  in 
  strata 
  which 
  have 
  been 
  meta- 
  

   morphosed 
  by 
  contact 
  with 
  eruptive 
  rocks, 
  and 
  have 
  proved 
  that 
  

   these' 
  graphite 
  crystals 
  have 
  originated 
  in 
  the 
  amorphous 
  coaly 
  

   substance 
  existing 
  originally 
  in 
  the 
  clay 
  slates 
  and 
  quartzose 
  

   schists. 
  In 
  the 
  Pirna 
  and 
  Kreischa 
  sections 
  in 
  Saxony, 
  there 
  are 
  

   upper 
  Silurian 
  clay 
  slates 
  and 
  quartz 
  schists 
  which 
  are 
  very 
  rich 
  

   in 
  carbon 
  particles 
  ; 
  these 
  slates 
  and 
  schists 
  lying 
  partly 
  within 
  

   the 
  region 
  of 
  contact 
  with 
  granite 
  and 
  syenite. 
  Now 
  it 
  is 
  within 
  

   this 
  contact-region 
  as 
  the 
  authors 
  have 
  shown, 
  that 
  these 
  strata 
  

   have 
  been 
  converted 
  into 
  rocks 
  rich 
  in 
  graphite. 
  For 
  the 
  exami- 
  

   nation, 
  they 
  used 
  a 
  very 
  rich 
  chiastolite 
  slate 
  and 
  a 
  graphite- 
  

   quartzite. 
  The 
  former 
  occurs 
  in 
  layers 
  in 
  the 
  highly 
  meta- 
  

   morphosed 
  upper 
  Silurian 
  grauwacke 
  of 
  Burkhardtswalde. 
  The 
  

   latter 
  is 
  a 
  genuine 
  contact 
  rock 
  in 
  the 
  immediate 
  vicinity 
  of 
  the 
  

   granite 
  and 
  occurs 
  in 
  the 
  Rohrsdorf 
  valley 
  near 
  Kreischa. 
  Both 
  

   these 
  rocks 
  have 
  come 
  from 
  the 
  original 
  quartz-schist, 
  their 
  struc- 
  

   ture 
  and 
  composition 
  alike 
  showing 
  them 
  to 
  be 
  true 
  contact- 
  

   products. 
  In 
  the 
  chiastolite 
  slate, 
  the 
  graphite 
  has 
  taken 
  the 
  

   place 
  of 
  the 
  finely 
  divided 
  coaly 
  substance 
  easily 
  combustible 
  in 
  

   the 
  Bunsen 
  flame 
  previously 
  existing 
  in 
  the 
  quartz-schist. 
  Iso- 
  

   lated 
  from 
  the 
  rock, 
  it 
  appeared 
  as 
  completely 
  opaque 
  irregular 
  

   masses 
  dark 
  gray 
  in 
  color 
  and 
  having 
  a 
  metallic 
  luster, 
  and 
  from 
  

   0*003 
  to 
  0*02 
  mm. 
  in 
  diameter 
  ; 
  the 
  carbon 
  particles 
  in 
  the 
  un- 
  

  

  