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PROF.  T.  G.  BONNET  ON  SOME  SCHISTOSE 
[Feb.  1893, 
It  is  generally  fine-grained,  but  a  few  flakes  of  a  chlorite-like 
mineral  and  specks  of  iron  oxide  and  pyrite  are  visible  on  close 
inspection.  In  a  slice  of  this  rock  we  find  the  same  constituents 
as  above,  but  there  is  less  chlorite  and  only  a  little  epidote,  while 
microliths  and  small  crystals  of  actinolite  are  abundant,  and  there 
are  grams  ot  a  brownish,  somewhat  dichioic  mineral,  possibly  an 
augite  in  process  of  change  to  hornblende.1  An  impure  sphene  is 
probably  associated  with  some  of  the  grains  of  iron  oxide,  and  not 
only  the  latter  mineral,  but  also  the  constituents  generally,  suggest 
crushing. 
The  result  then  of  crushing  some  thin  dykes,  which  were  probably 
once  dolentes  or  basalts,  has  been  to  produce  foliated  schists  in  \\  hich 
all  traces  of  the  original  structure  have  disappeared,  and  biotite  or 
chlorite  and  an  actinolitic  hornblende  have  replaced  the  original 
pyroxenic  constituent. 
Xext  we  may  briefly  notice  two  or  three  specimens  from  the 
larger  masses  of  ‘  green  schist.’  In  the  coarser  varieties  of  these 
(restricting  ourselves  to  the  Zermatt-Saas  district),  in  addition  to 
a  foliated  structure,  slight  indications  of  mineral  banding— not, 
however,  in  broad  stripes,  but  in  thin,  rather  irregular  lines — may  be 
sometimes  observed.  The  first  specimen,  a  moderately  foliated 
greyish-green  rock,  with  tiny  whitish  specks,  evidently  rich  in  a 
fibrous  hornblende,  represents  the  summit  of  the  Mittaghorn ;  it 
consists  mainly  of  actinolite,  epidote,  chlorite,  and  the  above-named 
water-clear  mineral,2  the  first  being  rather  abundant. 
The  next  specimen  is  a  rather  coarser  variety  of  the  (  green  schist  , 
slightly  more  fissile,  but  otherwise  very  similar  in  appearance  co  the 
last,  and  was  taken  from  the  Hinter  Allalin  Joch.3  Under  the  micro¬ 
scope  this  exhibits  a  very  definite  foliated  structure,  is  uch  in  actino¬ 
litic  hornblende,  with  a  fair  amount  of  epidote,  but  not  much  chlorite. 
The  water-clear  mineral  has  a  more  definitely  porphyritic  habit  than 
in  anv  previous  case,  and  one  or  two  grains  exhibit  a  poly  synthetic 
twinning,  like  a  plagioclase  felspar — the  extinction-angles  on  either 
side  of  the  twin-line  being  14°  or  less.  A  large  ‘  eye-shaped  ’  grain  of 
brownish-green  hornblende,  cut  transversely,  is  present  in  one  slide. 
This  has  every  appearance  of  being  an  original  constituent.  The 
rest  of  the  rock  seems  to  have  completely  recrystallized  subsequent 
to  the  crushing,  for  the  undulating  lines  of  actinolitic  and  other 
microliths  can  be  traced  right  through  the  grains  of  water-clear 
mineral. 
The  third  specimen  comes  from  the  southern  flank  of  the  ridge 
running  east  of  the  Hinter  Allalinhorn,  near  the  Hochlaub  Glacier. 
It  is  a  somewhat  banded  or  streaky,  not  very  fissile  rock,  in  which  a 
1  Sometimes  part  of  a  grain  is  greenish  blue  in  colour.  There  are  a  few 
microliths  of  rutile.  .  .. 
2  For  brevity  I  will  omit  the  minor  constituents  (such  as  iron  oxides,  rutile  or 
pseudobrookite,  zircon,  etc.,  some  of  which  are  usually  present),  since  they  hare 
no  bearing  on  the  main  subject  of  this  paper. 
3  A  pass  east  of  the  Hinter  Allalinhorn,  about  10,800  feet  above  sea-level,  cis- 
covered,  I  believe,  by  Mr.  Eccles. 
