360 
MESSES.  A.  HAEKEE  AXE  J.  E.  MAEE  ON  THE 
[Aug.  1893 
II.  Metamoephism  of  the  Basic  Bocks. 
In  their  non-metamorphosed  state  the  basic  lavas  of  this  district 
ditfer  from  the  intermediate  lavas  chiefly  by  being  richer  in  porphy- 
ritic  felspar,  and  that  of  a  basic  variety.  As  other  characteristic 
features,  we  may  note  in  some  examples  the  somewhat  greater 
abundance  of  iron  ores  and  the  presence  of  a  rhombic  as  well  as  a 
monoclinic  pyroxene.  The  rocks  have  undergone  to  a  considerable 
extent  the  ordinary  changes  included  under  the  term  4  weathering.* 
Of  the  resulting  secondary  products  some  (bastite,  kaolin,  etc.)  have 
remained  as  pseudomorphs  of  the  minerals  which  generated  them, 
while  others,  more  soluble,  have  become  disseminated  through  the 
mass  of  the  rock,  and  especially  collected  in  small  fissures  and  in  the 
vesicles  with  which  the  lavas  abound.  It  is  essential  to  bear  in 
mind  that  these  changes  were  effected  prior  to  the  metamorphism. 
We  hope  in  a  future  paper  to  describe,  from  another  part  of  the 
Lake  District,  the  thermal  metamorphism  of  comparatively  fresh 
basic  lavas  and  ashes.  In  the  ashes  accompanying  the  basic  lavas 
of  Shap  Bell  the  weathering-products  are  more  uniformly  dis¬ 
tributed,  and  metamorphism  has  developed  fewer  peculiarities ; 
indeed,  these  rocks  do  not  differ  so  much  from  the  andesitic  ashes  as 
to  demand  special  attention.  (See  PL  XVII.  fig.  5.) 
Another  change  which  the  rocks  under  consideration  have  under¬ 
gone,  though  not  universally,  is  that  resulting  in  cleavage.  This  is, 
as  might  be  expected,  most  marked  in  the  ashes,  and  seems  to  have 
often  determined  the  direction  of  the  foliation  which  these  show 
when  highly  metamorphosed.  Locally  the  lavas  have  also  been 
crushed,  though  in  less  degree.  The  cleavage  clearly  preceded  the 
metamorphism,  and  it  is  equally  clear  that  it  was  itself  preceded  by 
the  processes  which  filled  the  vesicles  of  the  lavas  with  weathering- 
products.  It  is  interesting  to  note  how,  in  one  and  the  same 
specimen,  those  vesicles  which  were  occupied  only  by  soft  materials 
were  completely  flattened,  while  those  filled  with  quartz  successfully 
resisted  deformation  [760 J.1  This  feature  is  to  be  seen  in  many 
parts  of  the  Lake  District,  and  has  been  remarked  by  Sir  Archibald 
Geikie.2 
The  first  clear  signs  of  metamorphism  are  seen  on  Low  Bell  at  a 
distance  of  1150  or  1200  yards  from  the  granite,  and,  as  usual,  in 
the  decomposition-products  of  the  rock.  One  slide  shows  little 
streaks  of  minute  flakes  of  brown  mica,  with  an  occasional  small 
crystal  of  sphene  [1279] ;  in  others  from  the  same  neighbourhood 
green  hornblende,  also  accompanied  by  sphene,  occurs  almost  to  the 
exclusion  of  the  mica  [759,  760].  Xearer  to  the  granite  the 
changes  increase  progressively,  those  in  the  contents  of  the  vesicles 
and  small  fissures  being  in  advance  of  those  in  the  body  of  the 
rock.  The  most  altered  examples  always  consist  entirely  of  mine¬ 
rals  produced  in  the  metamorphism,  and  present  the  clear,  fresh 
appearance  which  seems  to  be  so  characteristic. 
]  The  numbers  in  square  brackets  are  these  affixed  to  the  slides  in  the  col¬ 
lections  of  the  Woodwardian  Museum,  Cambridge. 
Pres.  Addr.,  Quart.  Journ.  Geol.  Soc.  vol.  xlvii.  (1891)  Proc.  p.  140. 
