154 
MISS  C.  A.  RAISIN  ON  VARIOLITE  OR 
[May  1893, 
and  stand  out  as  whitish  pimples  on  the  weathered  surface.  A 
diabase  is  also  exposed  in  the  farmyard  at  Dwyrhos,  where  the  vario- 
litic  structure  seems  to  be  connected  with  spheroids  (fig.  2,  p.  149). 
In  one  of  these,  about  1|  foot  in  diameter,  the  interior  is  compact 
and  pale  green,  surrounded  by  a  spherulitic  zone,  outside  which  the 
spheroid-crust  and  the  intervening  matrix  are  shiny,  dark  green, 
almost  black,  consisting  of  interfelted  chlorite  or  of  palagonite. 
The  variolite  at  Deunant  is  best  seen  in  the  quarry  behind  the  farm, 
where  the  rock  is  compact,  dark  green,  jointed,  and  slickensided. 
The  pale-green  oval  spherulites,  about  |  inch  in  length,  are  often 
ranged  end  to  end,  and  microscopic  examination  supports  the  idea 
that  the  elongation  is  in  the  direction  of  a  flow-structure,  but  this 
would  not  in  itself  disprove  the  intrusive  character  of  the  mass. 
North  of  Porth  Oer  beach,  as  previously  described,  a  purple 
basalt,  somewhat  calcareous  and  veined,  is  brecciated,  probably  by 
a  second  lawa-flow.  Both  rocks  exhibit  variolitic  structure.  I 
could  not  always  connect  it  with  the  exterior  of  spheroids,  although 
it  is  often  thus  developed.  Some  varioles,  perhaps  |  inch  in  length, 
not  radial  in  their  structure,  appear  to  consist  of  small  fragments 
of  the  breccia.  On  other  surfaces,  the  spherulites  appear  as  small 
knobs,  densely  crowded,  about  yx-_  inch  across,  which  in  the  field 
bear  a  resemblance  to  amygdules  contained  within  the  basalt.  In 
the  weathering  of  some  of  these  examples,  a  greenish  or  greyish 
envelope  flakes  off  from  a  reddened  centre.1  This  inner  kernel  is 
traversed  by  radial  bars  of  iron  oxide,  sometimes  grouped  like  iron 
filings  about  a  magnet.  The  deposit  is  wanting  in  the  outer  zone, 
where  the  felspathio  sheaves  are  more  distinct,  although  they  extend 
over  the  whole  spherulite,  giving  a  black  cross  in  polarized  light. 
An  outer  boundary,  roughly  elliptical  in  shape,  is  marked  by  a 
deposit  of  brightly  polarizing  granules,  and  similar  granules  are 
sparsely  scattered  over  the  section.  These  spherulites  are  grouped 
along  a  narrow  zone  in  the  rock,  and  gradations  can  be  traced  to  a 
mass  confusedly  intercrystallized  (PI.  I.  fig.  5).  The  specimen 
bears  much  resemblance  to  the  felsite  of  Arran  described  by  Prof. 
Bonney ; 2  but  in  the  Lleyn  slide  the  radial  structure  can  be  traced 
over  both  the  centre  and  the  external  zone  ;  and  the  granular 
boundary-line  is  not  polygonal  as  in  the  Arran  specimen,  although 
I  attribute  it  to  the  same  cause — contraction  of  the  rock  and  depo¬ 
sition  along  surfaces  of  weakness.  The  conditions  of  formation  in 
all  probability  were  similar,  since  here  the  second  flow  of  lava  may 
have  caused  renewed  heating  of  rock  partially  consolidated,  as 
described  by  Prof.  Bonney  in  Arran. 
At  Dinas-fach,  on  a  weathered  surface  of  dark  red  basalt  are  small, 
rather  elliptical  bodies  (averaging  \  inch  in  length)  paler  in  colour 
or  surrounded  by  a  paler  border.3  The  microscope  shows  that  iron 
1  The  partial  analysis  of  this  specimen  is  given  on  p.  148.  It  was  taken 
from  the  low  cliff,  near  the  isolated  boss  on  the  beach  described  on  p.  151,  note. 
2  G-eol.  Mag.  for  1877,  p.  510  and  fig.  3. 
3  Part  of  the  surface  exhibited  radiate  coral-like  markings,  which  were 
probably  limpet-tracks  similar  to  those  noted  by  the  Rev.  Edwin  Hill ;  see 
Quart.  Journ.  Geol.  Soc.  vol.  xlv.  (1889)  p.  387,  note. 
