HORNBLENDE  FROil  THE  BINNENTHAL. 
107 
Yoi.  49.] 
by  pressure.  Ought  we  not  to  say  the  same  of  the  garnet?  It 
must  he  later  than  the  opacite :  this  material,  however,  I  take 
to  be  a  very  early  constituent  ;  it  occurs  in  all  my  specimens,  hut 
with  less  regularity  in  those  which  show  most  crushing.  In 
some  cases  a  garnet,  or  part  of  it,  has  obviously  been  pulverized  and 
Fig.  1. — Secondary  development  of  biotite  in  a  crushed  schist,  x  30. 
reconstituted  1  ;  in  others  the  stratulae  of  opacite  lie  in  a  different 
direction  from  those  of  the  matrix.  80  I  think  that  in  the  Binnen- 
thal  rock  the  garnet  was  only  slightly  compressed,  without  material 
fracture,  and  the  stratulae  of  opacite,  already  present,  were  slightly 
flattened.  But  if  the  biotite- crystal  described  above  had  been 
already  formed  when  severe  pressure  was  applied,  it  must  have 
bent,  zigzagged,  or  split  open,  for  mica  is  a  mineral  ‘sensitive7  to 
pressure,  and  generally  retains  the  marks  of  maltreatment.  So 
1  consider  this  biotite  to  be  a  constituent  which  appeared  late  in 
the  history  of  the  rock,  though  very  probably  the  crystal  may  be 
reconstructed  from  the  ruins  of  a  former  one.  If  the  rock  had  been 
much  sheared  and  its  fragments  mingled,  then  scattered  films 
ought  to  have  been  produced,  as  has  happened  in  some  of  the  other 
instances.  Here  in  all  probability  the  crush  was  a  direct  one  ; 
still  the  molecules  must  have  travelled,  transverse  to  the  structure 
of  the  rock,  for  some  little  distance,  in  order  to  build  up  a  crystal 
such  as  that  which  has  been  described. 
The  next  instance  of  constructive  crystalline  action  seems  to  me 
still  more  remarkable.  The  specimen  was  obtained  by  Mr.  J.  Eccles 
on  the  Hohsandhorn,  near  the  summit  (10,515  feet).  I  have  not 
ascended  the  peak,  but  have  seen  it  from  the  summit  of  the  neigh¬ 
bouring  Ofenhorn  (10,728  feet)  and  from  a  pass  (about  9400  feet) 
over  the  connecting  ridge.  This  is  gneiss,  but  the  peak  of  the 
Hohsandhorn  is  formed  of  the  dark-mica  schists  mentioned  above, 
which  are  parted  by  a  zone  of  marble.  The  matrix  of  the  specimen, 
1  See  Quart  Journ.  G-eol.  Soc.  vol.  xliv.  (1888)  pi.  xv.  (Attwoodon  ‘  Geology 
of  Mysore  ’)  for  excellent  representations  of  crushed  and  flattened  garnet.  Parts 
of  fig.  1  (the  schist),  though  much  more  quartzose,  give  some  idea  of  the 
‘fibrous’  structure  referred  to  in  this  paper.  Both  it  arid  fig.  2  represent  the 
mode  in  which  the  quartz  and  biotite  get  ‘  mixed  up  ’  in  another  mineral. 
