Yol.  49.] 
CRYSTALLINE  SCHISTS  OE  THE  MALVERN  HILLS. 
399 
probably  secondary  products ;  but  the  first  and  second  have  been 
noticed  in  No.  II.,  while  the  last  occurs  in  very  inconspicuous  pro¬ 
portion. 
Particulars  of  dips  and  strikes,  and  details  of  rock-distribution, 
will  be  found  in  Dr.  Hoiks  memoir,1  and  descriptions  of  the 
principal  rock-types  in  Mr.  Rutley’s  paper.2 
I  have  to  express  my  great  obligations  to  Messrs.  J.  H.  Player 
and  T.  H.  Waller  for  chemical  analyses  ;  also  to  Dr.  G.  H.  Bailey 
and  Dr.  Cohen,  of  the  Owens  College,  Manchester,  for  superintending 
several  analyses. 
II.  Confirmation  from  other  Sources  of  some  Points 
in  the  Author’s  former  Papers. 
Secondary  Minerals  produced  during  Dynamo-Metamorphism. — 
Prof.  G.  H.  Williams,  in  describing  the  k  Greenstone-schist  Areas 
of  the  Menominee  and  Marquette  Regions  of  Michigan,’  Bull.  U.S. 
Geol.  Surv.  1891,  No.  62,  states  that  the  new  minerals  formed 
during  the  production  of  these  schists  are  albite,  microcline,  zoisite, 
garnet,  quartz,  hornblende,  epidote,  biotite,  muscovite,  sericite, 
rutile,  anatase,  and  sphene. 
This  list  corresponds  with  that  of  the  secondary  minerals  recog¬ 
nized  by  me  in  the  Malvern  schists  (No.  II.),  except  that  the 
secondary  plagioclastic  felspar  of  my  papers  could  not  be  specifically 
identified,  owing  to  its  minutely-granular  structure  ;  but  as  the 
rock  containing  it  is  sometimes  almost  destitute  of  lime,  much  of 
it  may  safety  be  referred  to  albite.  Prof.  Williams  mentions 
anatase,  which  I  have  not  recognized  at  Malvern,  and,  on  the 
other  hand,  my  list  includes  calcite,  chlorite,  and  iron  oxides,  but 
these  are  of  course  very  commonly  produced  in  rock-crushing. 
Production  of  Secondary  Biotite. — The  conversion  of  Chlorite 
into  Biotite  is  recorded  by  Salomon,  Zeitschr.  d.  Deutsch.  geol. 
Gesellsch.  vol.  xlii.  (1890)  p.  450  ;  also  by  Lossen,  Congres  Geol. 
Internat.  Londres  1888,  Compte-Rendu,  p.  180,  and  Riidermann, 
Neues  Jahrb.  v.  Beilage-Band  (1887)  p.  643. 
The  formation  of  Biotite  out  of  Chlorite  and  Sericite  is  asserted 
by  M.  A.  Michel-Levy  (‘  Sur  POrigine  des  Terrains  cristallins 
primitifs,’  p.  58,  Congres  Geol.  Internat.  Londres,  1888). 
The  production  of  Biotite  in  Shear-zones,  when  none  of  that 
mineral  occurs  in  the  walls  of  the  shear-zones,  is  recorded  by 
Mr.  J.  K.  Kemp  in  a  paper  on  4  The  Great  Shear-zone  near  Avalanche 
Lake  in  the  Adirondacks,’  Amer.  Journ.  Sci.  vol.  xliv.  (1892)  p.  109. 
Production  of  Muscovite  from  Biotite. — This  change  has  been 
actually  effected  in  the  laboratory  by  Mr.  Alex.  Johnstone 
(‘  Nature,’  vol.  xlvi.  Sept.  29th,  1892,  p.  518).  Mr.  Johnstone 
states  that  “  by  the  continued  action  of  carbonic  acid,  oxygen,  and 
water,  biotite  loses  magnesia  (taken  out  as  carbonate),  and  iron 
(removed  either  as  oxide  or  carbonate),  and  becomes  eventually  the 
1  Quart.  Journ.  Geol.  Soc.  vol.  xxi.  (1865)  p.  72.  - 
2  Ibid.  vol.  xliii.  (1887)  p.  481. 
