Yol.  49.]  CRYSTALLINE  SCHISTS  OF  THE  MALVERN  HILLS.  419 
44  any  ordinary  hydro-biotite,  Snell  as  voigtite,  vermiculite,  or  pyro- 
sclerite,  exposed  for  a  lengthened  period  to  the  action  of  carbonic- 
acid  water,  invariably  lost  a  portion  of  its  magnesia  (and  iron).” 
This  investigation  has  been  continued,  and  the  results  are  sum¬ 
marized  in  Section  II.  of  the  present  paper  (p.  399).  It  is  fair  to 
assume  that,  at  higher  temperatures,  to  say  nothing  of  pressures, 
the  action  of  carbonated  waters  would  he  still  more  energetic. 
The  elimination  of  magnesia  during  the  shearing-process  seems  to 
he  absolutely  demonstrated  by  the  Malvern  sections.  No  one  who 
examines,  for  example,  the  section  at  the  southern  end  of  Magged 
Stone  Hill,  and  studies  a  series  of  the  rocks  under  the  micro¬ 
scope,  can  doubt  that  the  sericite-gneiss  was  once  a  diorite.  Yet 
the  percentage  of  magnesia  has  fallen  from  5  in  the  diorite  to  less 
than  1  in  the  schist.  This  is  seen  in  the  following  analyses,  the 
first  four  of  which  were  very  kindly  determined  for  me  by 
Mr.  J.  H.  Player. 
The  specimens  II.,  III.,  IV.  are  taken  along  the  section  from 
crushed  diorite  to  schist.  For  comparison  I  append  the  composition 
of  the  same  variety  of  diorite  in  an  uncrushed  state  (I.)  from 
another  Malvern  locality. 
I. 
II. 
III. 
IY. 
Silica  . 
.  47-6 
49-0 
52-8 
61  *6 
Alumina  . 
.  17-6 
190 
15-8 
18*6 
Titanic  oxide  . 
.  1*6 
1*2 
2-6 
•8 
Ferric  oxide  . 
.  4-8 
3-4 
54 
1*3 
Ferrous  oxide  . 
.  5-8 
7-5 
9-5 
51 
Lime  . 
.  8-6 
2-8 
*5 
•2 
Magnesia  . 
.  5-0 
5-3 
41 
2-6 
Soda  . . 
.  2-3 
20 
m 
1*6 
Potash  . 
.  4*3 
2*5 
1*9 
3*7 
Loss  . 
.  2*2 
6*5 
5-7 
37 
99-8 
99-2 
996 
99-2 
I.  A  typical  specimen  of  the  coarse-grey  diorite. 
II.  The  same  variety  crushed  (taken  near  specimen  No.  273),  being  a  sort  of 
grit  composed  of  fragments  of  felspar  in  a  groundmass  of  chlorite, 
biotite,  and  ferruginous  dust. 
III.  The  grit  just  before  it  passes  into  schist.  The  rock  has  undergone  partial 
reconstruction,  the  iron  oxide  has  been  recrystallized,  and  there  is  some 
free  quartz.  Sphene  is  in  unusual  proportion. 
IY.  Sericite-gneiss,  containing  some  chlorite.  It  is  within  one  foot  of  No.  III. 
in  the  same  mass,  and  an  intermediate  specimen  furnishes  the  slide 
(303)  in  which  the  actual  gradation  between  grit  and  schist  is  seen. 
This  analysis  would  give  (roughly)  the  following  percentages  : — Chlo¬ 
rite  =  10,  white  mica  =  25,  orthoclase  (or  microcline,  or  both)  =  15, 
albite  =  15,  iron  oxide  =  5,  quartz  =  25,  which  corresponds  very  well 
with  the  appearance  of  the  rock  under  the  microscope. 
It  will  be  seen  that  in  this  series  the  silica  rises  in  steps  thus  : — - 
47*6,  49-0,  52-8,  61*6.  Two  analyses  of  other  portions  of  No.  IY., 
made  for  me  at  Owens  College  by  the  kindness  of  Dr.  Cohen,  give 
the  silica  percentages  respectively  as  64*96  and  73*13.  The  lime 
in  the  above  series  falls  in  steps  thus : — 8*6,  2*8,  0*5,  0*2.  The 
magnesia  also  falls,  but  less  rapidly,  thus  : — 5*0,  5*3,  4*1,  2*6. 
No.  IY.  contains  a  fair  quantity  of  chlorite;  but  Dr.  Cohen’s 
