EXPLANATION  OF  PLATE  XVII. 
( The  figures  are  all  drawn  in  natural  light  and  magnified  20  diameters.  The 
numbers  in  brackets  [  J  refer  to  the  slides.) 
Fig.  1.  [1748]  Portion  of  a  large  amygdule  in  a  loose  block  of  metamorphosed 
basic  lava,  north  of  the  granite  mass.  In  the  upper  part  of  the  figure 
is  a  large  crystal  of  epidote,  bounded  on  the  right  by  clear  quartz, 
on  the  left  by  calcite.  The  latter  is  penetrated  in  the  lower  part  of 
the  figure  by  needlesof  amphibole,  and  to  the  right  of  this  is  a  plate  of 
augite  enclosing  grains  of  epidote. 
Fig.  2.  [1750]  Another  amygdule  in  the  same.  In  the  lower  left-hand  quarter 
is  a  plate  of  augite  with  intergrown  needles  of  amphibole.  Similar 
needles,  in  parallel  position,  penetrate  the  calcite  which  occupies  the  cen¬ 
tral  part  of  the  figure.  Above  to  the  right  is  garnet,  to  the  left  quartz. 
Fig.  3.  [1749]  Another  amygdule  in  the  same.  A  cluster  of  garnet-crystals, 
some  showing  zonary  growth  :  patches  of  calcite  occur  interstitially. 
Fig.  4.  [1747]  Anotheramygdule  in  the  same.  An  intricate  admixture  of  garnet 
and  calcite,  the  garnet  bounded  on  the  right  by  a  large  epidote-plate 
enclosing  two  imperfect  crystals  of  sphene.  Above  these  is  a  crystal 
of  augite  with  parallel  intergrowth  of  amphibole-needles,  some  of  which 
extend  as  a  fringe  into  the  epidote.  Pyrites  and  quartz  are  also  seen. 
Fig.  5.  [89(3]  Highly  metamorphosed  ash  associated  with  basic  lavas,  Poorhag 
Gill ;  very  near  the  granite.  Flakes  of  brown  mica  with  partial 
parallel  disposition  are  scattered  thickly  tlmough  a  clear,  very  fine¬ 
grained  mosaic,  essentially  of  felspar.  The  relatively  clear  space  marks 
the  position  of  a  felspar-crystal  recrystallized  into  an  aggregate  of 
rather  less  fine  texture  than  the  matrix. 
Fig.  6.  [174b]  Portion  of  highly  metamorphosed  Lower  Caniston  Limestone 
at  Wasdale  Head  ;  about  100  yards  from  the  granite.  The  slide 
shows  part  of  the  light-coloured  border  of  one  of  the  idocrase-nodules 
in  the  marble  described  on  p.  368.  Striated  felspar  occurs  in  relatively 
large  plates,  as  well  as  in  small  grains  ;  with  it,  in  subordinate  quantity, 
is  a  monoclinic  pyroxene  ;  the  opaque  mineral  is  apparently  pyrites. 
Discussion. 
The  President  congratulated  the  Authors  on  this  important 
addition  to  their  previous  communication.  In  some  respects  this 
paper  was  the  antithesis  of  the  one  which  had  just  been  read  (Dr. 
Callaway’s),  for  the  Authors  limited  the  area  in  which  metasomatic 
change  took  place  to  a  fraction  of  an  inch. 
Mr.  Kutley  considered  that  the  statements  made  by  the  Authors 
regarding  the  development  of  certain  minerals  in  the  altered  rocks 
were  of  great  value.  Concerning  the  absence  of  reaction  between  the 
calcite  in  the  amygdaloids  and  the  silicates  which  occurred  in  close 
proximity,  he  cited  a  case  in  which  the  molecular  rearrangement 
brought  about  by  the  conversion  of  a  piece  of  flashed  glass  into  a 
crystalline  mass  had  caused  scarcely  any  disturbance  of  the  coloured 
film.  The  statements  relating  to  the  development  of  epidote  were 
important,  since,  so  far  as  he  was  aware,  that  mineral  had  not  yet 
been  artificially  reproduced. 
Mr.  Teall  was  especially  interested  in  that  portion  of  the  commu¬ 
nication  which  dealt  with  the  change  brought  about  in  the  calcareous 
portions  of  the  rocks.  The  silicates  there  produced  were  allied  to 
those  found  in  crystalline  limestones  associated  with  gneisses  and 
schists,  and  the  work  of  the  Authors  might  therefore  throw  light 
on  the  conditions  under  which  these  rocks  were  produced. 
Mr.  Haeker,  in  reply  to  Mr.  Kutley,  said  that  the  epidote  described 
as  occurring  in  the  metamorphosed  basic  lavas  was  found  chiefly  in 
the  outer  parts  of  the  large  amygdules  and  in  the  rock  bordering  the 
amygdules.  It  was  undoubtedly  a  product-of  thermal  metamorphism. 
Mr.  Marr  also  spoke. 
