Yol.  49.] 
VAEIOLITE  OF  THE  LLEYX. 
145 
10.  Yakiolite  of  the  Lleyx,  and  associated  Yolcaxic  Bocks.  By 
Miss  Catheeixe  A.  Baisih,  B.Sc.  (Communicated  by  Prof. 
T.  G.  Bohney,  D.Sc.,  LL.D.,  F.B.S.,  Y.P.G.S.  Bead  January 
11th,  1893.) 
[Plate  I.] 
Contents. 
I.  Introduction  . 
II.  Lithological  Characters  of  the  Igneous  Bocks 
III.  Spheroidal  Structure . 
IV.  Fluidal  Structure  and  Flow-brecciation  . 
Y.  Yariolite . 
(a)  General  Microscopic  Structure. 
(b)  Distribution. 
(e)  Development. 
VI.  Pseudocrystallites . 
VII.  Secondary  Minerals  . 
VIII.  Stratigraphical  Summary  of  the  District  .... 
Page 
145 
146 
148 
151 
152 
158 
158 
160 
I.  Inteoductiox. 
Although  much  has  now  been  written  about  the  igneous  rocks  of 
the  Lleyn,  especially  in  Mr.  Alfred  Harker’s  valuable  essay,1  yet,  as 
he  expressly  excludes  most  of  the  district  of  which  I  am  treating, 
and  as  it  receives  only  slight  mention  in  other  writings,  some  of  the 
most  interesting  examples  from  the  part  coloured  on  the  Geological 
Survey  map  as  ‘  metamorphosed  Cambrian  ’  have  remained  un¬ 
noticed.  I  have  therefore  put  together  a  few  notes  on  the  rocks 
which  I  have  collected  in  the  course  of  many  visits  during  the  last 
six  years.  The  specimens  not  hitherto  described  include  a  variolite 
— a  spherulitic,  somewhat  basic  rock.  A  short  summary  of  its 
occurrence  will  at  least  serve  to  show  that  we  have  on  the  main¬ 
land  of  our  island  (apart  from  any  example  in  Anglesey 2)  a  mass 
of  variolitic  diabase  with  characters  very  similar  to  those  of  German 
and  Alpine  localities,  corresponding  closely  in  many  particulars  with 
that  graphically  described  by  Mr.  J.  W.  Gregory  from  the  Fichtel- 
gebirge,3  and  also,  although  perhaps  less  markedly,  with  that  of  the 
Durance,  as  shown  by  Prof.  Cole  and  Mr.  Gregory.4  I  am  limiting 
myself  mainly  to  the  rocks  which  can  be  clearly  recognized  as 
igneous,  and  have  given  only  a  short  notice  of  others  in  the  last 
section  of  the  present  paper.  The  extensive  masses  of  a  rather 
indefinite  and  schistose  character  in  many  parts  are  ashy  or 
1  ‘  The  Bala  Volcanic  Series  of  Caernarvorshire  and  Associated  Bocks,’ 
Cambridge,  1889. 
2  See  Quart.  Journ.  Geol.  Soc.  vol.  xlvi.  (1890)  p.  331,  note;  also  £  The  Vario¬ 
lite  of  Ceryg  Gwladys,  Anglesey,’  G.  A.  J.  Cole,  Sci.  Proc.  Boy.  Dub.  Soc. 
vol.  vii.  (1891)  p.  112. 
3  Quart.  Journ.  Geol.  Soc.  vol.  xlvii.  (1891)  p.  45. 
4  Ibid.  vol.  xlvi.  (1890)  p.  295. 
Q.  J.  G.  S.  No.  194. 
L 
