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PROF.  T.  G.  BOHNEY  ON  SOME  SCHISTOSE  [Feb.  1893, 
like  the  lids  round  the  ball  of  the  eye.  Both  rocks  have  been 
affected  by  pressure,  which  has  acted  roughly  at  right  angles  to  the 
banding  of  the  calc-schist.  It  has  crushed  the  ‘ greenstone’  generally 
into  a  4  papery  ’  mass,  but  one  or  two  bits,  which  have  suffered  less 
severely,  present  a  general  resemblance  to  the  4  green  schist’  of  the 
peak.1  *  The  specimen  taken  is,  macroscopically,  a  rather  fissile, 
faintly  speckled,  dull-green  and  warm-grey  coloured  rock,  containing 
a  considerable  amount  of  a  mineral  resembling  chlorite.  Micro¬ 
scopic  examination  shows  that  this  mineral  has  one  well-marked 
cleavage,  and  occurs  in  fairly  thick  flakes  with  irregularly  projecting 
edges  and  without  any  definite  crystalline  form.  The  colour  in 
ordinary  light  is  a  verj^  pale  sea-green.  The  dichroism  is  not 
strong :  with  vibrations  in  the  direction  of  the  cleavage  the  mineral 
is  either  colourless  or  a  very  faint  straw  tint ;  with  vibrations  per¬ 
pendicular  to  the  cleavage,  a  pale  olive-green.  With  crossed  nicoff 
the  tints  are  of  a  low  order,  the  brightest  being  a  greyish-white,  and 
extinction  is  parallel  with  the  cleavage.  The  mineral  is  occasionally 
associated  with  small  flakes  of  biotite,  into  which  it  sometimes  seems 
to  pass,  so  that  part  at  least  of  it  may  be  a  hydrous  form  of  that 
mineral  rather  than  a  true  chlorite.  Epidote  is  fairly  abundant, 
occurring  in  various  shapes,  from  grains  to  moderately-regular 
prisms  with  a  well-developed  basal  cleavage.  With  transmitted 
light  it  is  practically  colourless ;  with  crossed  nicols  the  tints  are 
often  brilliant.  An  actinolitic  hornblende  is  present,  but  is  small 
and  not  very  abundant.  Here  and  there  are  grains  of  calc-ite  and 
some  granules  of  iron  oxide,  with  occasionally  a  dusty-looking 
mineral,  sometimes  aggregated,  probably  sphene ;  possibly  also  a 
few  microliths  of  zircon.  One  rather  abundaut  constituent 
still  remains.  It  commonly  occurs  in  roundish  or  somewhat 
prismatic  grains,  up  to  about  *05  inch  in  the  longer  diameter, 
water-clear  and  very  free  from  cavities,  except  a  few  extremely 
minute,  but  frequently  enclosing  microliths  of  the  chlorite,  epidote, 
and  actinolite.  It  does  not  present  any  distinct  cleavage  or  any  sure 
outline  of  a  crystal-face,  but  if  we  may  trust  certain  faint  indications 
of  the  former  the  extinction  is  oblique.  The  colours  are  like  those 
of  quartz,  but  sometimes  even  richer.  It  presents  many  resem¬ 
blances  to  that  mineral,  and  some  to  kyanite,  but  on  the  whole  I 
incline  to  regard  most  of  it  (for  some  of  the  smaller  grains  may  be 
quartz)  as  a  felspar.  Both  its  inclusions  and  its  relations  to  the 
larger  constituents  indicate  that  this  was  one  of  the  last  formed 
minerals.  The  constituents  exhibit  some  orientation,  and  the  rock 
would  be  accepted  without  hesitation  as  a  crystalline  schist ;  yet 
1  On  the  Swiss  Survey  Map  (Sheet  XXIII.)  this  and  about  half  the  ridge 
connecting  it  with  the  Egginerkorn  (11.080  feet)  is  coloured  as  gneiss.  That  rock 
undoubtedly  occurs  on  the  flank  of  the  Mittagliorn  ;  but  the  summit  consists  of 
‘  green  schist,’  and  this  rock,  with  calc-schist,  so  far  as  I  could  see,  dominates  on 
the  upper  part.  I  ascended  the  two  peaks  on  different  days  and  did  not  traverse 
the  long  ridge  between  them,  but  have  no  reason  to  doubt  that  all  the  upper 
part  of  this  mountain-mass  consists  of  the  ‘  green  schist,’  though  atany  moment 
one  might  come  upon  serpentine  (of  which,  however,  there  is  not  likely  to  be 
much)  or  upon  a  small  infold  of  calc-schist. 
