404  DR.  C.  CALLAWAY  ON  THE  ORIGIN  OE  THE  [Allg.  I  893, 
veins  of  felsite  appear  in  the  western  surface.  In  the  lower  face  of 
the  rock  the  diorite  is  quite  recognizable  as  the  coarse-grey  variety 
(No.  3),  but  is  rather  crushed  and  decomposed.  Following  this 
rock  up  the  slope,  we  see  that  the  crushing  and  rottenness  increase, 
while  aggregation  of  the  constituents  becomes  very  marked.  Thus, 
one  hand-specimen  is  nearly  all  crushed  felspar,  with  perhaps  some 
infiltrated  calcite  and  chlorite ;  another  is  mostly  chlorite ;  in  a 
third,  iron  oxide  predominates.  Near  the  top  of  the  slope,  a  little 
to  the  left  of  the  buttress,  a  rough  schistosity  sets  in.  Felspar 
in  small  irregular  fragments,  sometimes  in  recognizable  portions 
of  the  crystals,  lies  in  narrow  parallel  seams.  The  groundmass  is 
chlorite,  passing  into  brown  mica,  with  a  great  quantity  of  opaque 
dust,  presumably  iron  oxide.  The  rock  is  curiously  suggestive  of  a 
true  sedimentary  grit.  Much  of  it  is  very  rotten,  and  specimens 
for  the  microscope  are  hard  to  get. 
For  several  yards  to  the  west  there  is  little  change.  Then  the 
outcrop  is  interrupted  by  soil  and  debris,  hut  the  exposures  show 
that  the  rock  is  becoming  more  and  more  comminuted.  Masses 
of  felsite  appear  here  and  there  up  to  the  end  of  the  section,  but  no 
more  granite  is  seen,  though  there  is  plenty  on  the  southern  side  of 
the  quarry.  Just  before  the  Hollybush  Sandstone  is  reached, 
marked  reconstruction  sets  in.  The  rock  becomes  clearer  and 
sounder,  and  the  schistosity  more  strongly  marked.  The  last 
series  of  changes  is  best  observed  by  leaving  the  quarry  and 
ascending  the  spur  :  the  gradation  from  grit  to  schist  is  seen  at 
many  points  on  the  ridge.  Yeins  of  granite  sometimes  appear  in 
the  schist,  and  are  sheared  out  into  bands  of  thinly  foliated,  con¬ 
torted  gneiss.  A  little  south  of  the  western  summit,  granite  also 
veins  the  grit,  hut  is  not  schistose.  Just  at  the  western  summit, 
the  passage  from  grit  to  schist  may  be  seen  in  the  same  hand- 
specimen,  and  even  in  the  same  slide.  A  series  of  micro-slides  in 
my  collection  illustrates  the  above  general  description. 
There  is  so  much  crushing  and  decomposition  in  the  rocks  of  this 
locality  that  I  have  been  unable  to  obtain  a  specimen  of  the  diorite 
that  is  unaltered.  There  is  no  doubt,  however,  that  it  is  a 
modified  form  of  the  rock  which  Mr.  Rutley  has  described 1  as  a 
4  hornblende-gabbro.’ 
Slides  Nos.  454,  455,  and  456  (fig.  1). — These  specimens  are 
taken  from  the  lower  part  of  the  projecting  wall,  and  differ  very 
slightly  from  each  other  and  from  Mr.  Eutley’s  type.  The  horn¬ 
blende  shows  very  clearly  the  prismatic  cleavages,  hut  is  much 
crushed  and  distorted.  Here  and  there  it  has  been  changed  into 
chlorite,  especially  along  the  cleavages.  The  chlorite  is  pale  green 
in  ordinary  light,  shows  slight  pleochroism,  and  under  crossed  nicols 
is  nearly  black  with  slight  mottlings  of  grey.  Epidote  is  abundant : 
it  is  usually  in  dirty  aggregates  without  regular  boundaries  to  the 
individual  granules.  There  is  a  little  white  mica  in  minute  flakes  : 
it  is  clearly  secondary,  being  moulded  on  the  contours  of  the 
epidote  and  the  jagged  projections  of  the  broken  hornblende-prisms. 
1  Quart.  Journ.  Geol.  Soc.  vol.  xliii.  (1887)  p.  493. 
