100 
PROF.  T.  &.  BONNET  OX  SOME  SCHISTOSE 
[Feb. 1893, 
abundant;  it  has  a  tendency  to  aggregation,  for  in  parts  of  the 
slide  it  is  almost  absent ;  it  has  formed  after  the  hornblende,  to 
which  it  forms  a  kind  of  ‘  setting.5  There  are  grains  of  iron  oxide, 
part  at  least  haematite  and  limonite,  and  of  an  almost  opaque,  brown¬ 
ish,  granular  substance  which  also  occurs  in  streaks  (the  residue  ot 
more  or  less  crushed  felspar  ?).  These  minerals  appear  to  be  set 
in  a  water-clear  ground,  which,  on  using  crossed  nicols,  breaks  up 
into  a  rather  irregular  granular  mass,  the  individuals  having  a 
rather  polygonal  outline.  These,  though  their  tints  are  somewhat- 
less  brilliant,  may  be  identical  with  the  secondary  felspar  already 
mentioned.  The  constituents  of  the  rock  exhibit  a  fairly  marked 
orientation. 
The  second  specimen,  fromKehlmatten  near  Binn,1 2  is  a  dull-green, 
fairly  strong  and  solid  schist,  containing  some  flakes  of  biotite,  and 
marked  in  parts  by  fine  white  lines,  which  correspond  with  a 
slight  fissility.  Under  the  microscope  the  hornblende  is  seen  to  be 
more  acicular.  rather  smaller  in  size,  but  of  a  deeper  blue-green  colour 
and  more  definitely  orientated  than  in  the  last  case :  epidote  as 
before.  The  flakes  of  biotite  are  larger,  more  scattered,  and  in¬ 
clude  both  these  minerals ;  they  do  not  stand  in  any  definite 
relation  to  the  foliation— in  this  rock  very  well  marked — for  many 
flakes  lie  more  or  less  transversely  1o  it.  The  water-clear  mineral 
occurs  both  in  patches  and  in  streaks,  and  is  more  variable  in  size ; 
some  of  the  grains  undoubtedly  show  polysynthetic  twinning,  others 
a  ‘  clustered 5  structure  ;  quartz  may  be  present,  but  most  of  them  are 
more  probably  a  felspar  (secondary)  :  here  mechanical  disturbance  is 
suggested  even  more  definitely  than  in  the  last  case,  and  one  of  the 
streaks  exhibits  small  flexures. 
The  third  specimen,  from  a  mass  of  rock  which  is  exposed  in 
the  bed  of  the  river,  opposite  Giessen,  near  Binn,'  is  rather 
similar  to  the  last  one,  but  is  without  the  white  streaks  and  has 
more  biotite,  which  dominates  in  fairly  well-marked  bands.  The 
same  minerals  are  present  as  in  the  two  previously-described 
specimens,  with  a  more  definitely  banded  arrangement.  Here 
also  some  of  the  clear  mineral  shows  plagioclastic  shaping.3  While 
most  of  the  constituents  have  a  roughly  parallel  ordering,  some  ot 
the  biotite,  especially  in  the  case  of  the  larger  flakes,  seems  to  be 
quite  independent. 
1  Probably  this  rock  and  that  at  Giessen  are  portions  of  one  and  the  same 
nearly  vertical  dyke,  striking  iN.E.  and  S.W.,  the  continuation  of  which  in  the 
latter  direction  is  seen  under  the  Hotel  at  Binn  and  at  several  points  between 
that  village  and  Giessen.  At  Kehlmatten,  in  two  exposures  the  vein  varies 
from  15  to  70  feet  in  thickness,  is  very  schistose,  and  its  cleavage  is  identical  in 
direction  with  that  of  the  corresponding  Calc-Schiefer ;  the  schists  and  limestones 
in  contact  with  the  dyke  are  rather  altered,  and  some  of  the  latter  have  been 
caught  up  in  the  hornblende-rock. — J.  Eccles. 
2  Here  the  rock  is  120  feet  thick,  much  crushed  and  contorted,  in  short  a 
hornblende-schist,  conforming  (like  the  last)  in  its  cleavage  with  the  surrounding 
schists.  Evidently  the  rock,  after  penetrating  the  older  Calc-Schiefer,  has  been 
subjected  with  them  to  one  and  the  same  pressure. —  J.  Eccles. 
3  This  rock  is  exceptionally  rich  in  rutile  and  pseudobrookite. 
