Tol.  49.]  THE  LLEYN,  AND  ASSOCIATED  VOLCANIC  ROCKS.  155 
oxide  is  concentrated  in  the  centre ;  but  the  spherulite  has  very 
little  radial  structure.  The  variolite  is  found  between  the  mass- 
of  green  diabase  forming  the  islet  and  the  breccia  containing 
spherulitic  fragments,  so  that  here  also  it  appears  to  have  relations 
with  a  complex  of  igneous  rocks. 
In  the  promontory  south  of  Porth  Orion  the  varioles  are  clearly 
connected  with  spheroids  of  the  rock,  recalling  the  description  given 
by  Mr.  J.  W.  Gregory  of  a  similar  mass  at  Berneck.1  The  interior 
of  the  spheroids  is  purplish  in  colour  or  mottled :  the  exterior  is 
generally  green,  surrounding  a  reddened  zone.  Spherulites  deve¬ 
loped  quite  at  the  outside  are  small  and  close,  but  the  examples 
which  at  once  attract  attention  on  the  cliff  and  on  scattered  blocks 
belong  to  that  part  of  the  spheroid  where  the  green  zone  is  passing 
to  the  next  redder  band  (fig.  3,  a,  p.  150).  These  spherulites  average 
about  |  inch  in  diameter,  standing  out  like  peas  on  the  weathered 
surface,  and  they  are  divided  generally  into  a  green  rim  and  a  red 
interior,  but  the  red  colour  in  some  is  confined  to  a  central  speck, 
in  others  extends  over  the  whole.2  The  spherulites  possess  a 
shadowy  radial  structure,  but  no  distinct  mineral  forms,  while  in 
the  interior  of  the  spheroid  the  constituents  of  the  rock  become 
better  defined,  but  closely  intercrystallized.3  Badial  groups  starting 
from  adjacent  centres  are  confusedly  interlocked,  and  the  spherulitic 
habit  is  only  discovered  by  microscopic  examination. 
The  same  relations  in  more  rudimentary  structures  are  found 
in  the  spheroidal  diabase  of  Porth-din-lleyn  on  the  north,  and  of 
Pared-llech-y-menyn  on  the  south.  At  the  former  place,  the 
spherulitic  tendency  in  rocks  which  are  not  variolites  was  noted  by 
Prof.  Bonney,  and  he  also  described  the  spheroidal  character  well 
exhibited  at  certain  parts.  The  two  structures  are  sometimes 
related.  Near  the  outer  boundary  in  one  spheroid,4  a  greenish 
palagonite  includes  small  microporphyritic  felspars,  around  which 
granular  aggregations  are  clustered.  These  seem  to  form  incipient 
spherulitic  or  axiolitic  structures  (PI.  I.  fig.  6).  Within  this  narrow 
peripheral  zone,  the  spheroid  is  a  confused  mass  of  similar  micro- 
lithic  growth,  as  if  the  crystallization  took  place  more  slowly  and 
uniformly  ;  and  about  an  inch  from  the  outer  surface  is  a  band  of 
small,  irregular,  sometimes  radial  cavities. 
(c)  Development. — Yariolite  has  been  defined  as  a  “  devitrified 
spherulitic  tachylyte,  typically  coarse  in  structure.”  5  I  take  the 
last  phrase  to  mean  : — -with  spherulites  visib  e  macroscopically,  since 
the  microscope  shows  complete  gradations  to  rocks  with  no  spheru¬ 
litic  tendency.  The  term  thus  retains  its  original  connotation  given 
in  pre-microscopic  days.  Distinct  spherulites,  whether  in  acid  or 
1  Ibid.  vol.  xlvii.  (1891)  p.  48,  fig.  2. 
2  These  appear  to  be  very  similar  to  those  of  Annalong,  Co.  Down,  judging 
from  Prof.  Cole’s  description,  Sci.  Proc.  Poy.  Dub.  Soc.  vol.  vii.  (1892)  p.  513. 
3  Cole  and  Gregory,  Quart.  Journ.  Geol.  Soc.  vol.  xlvi.  (1890)  p.  313  and 
pi.  xiii.  fig.  5. 
4  Obtained  from  the  cliff  near  the  boathouse. 
5  Cole  and  Gregory,  op.  cit.  p.  330. 
