166 
THE  DISTKICT  WEST  OF  CAEEMAETHEN. 
[May  1893. 
11.  Notes  on  the  Geology  of  the  Disteict  West  of  Caeemaetheh. 
Compiled  from  the  Notes  of  the  late  T.  Robeets,  Escp,  M.A., 
F.G.S.  (Communicated  by  Prof.  T.  McKehny  Hughes,  M.A., 
F.R.S.,  F.G.S.  Head  February  8th,  1893.) 
The  following  paper  has  been  written  by  Mr.  J.  E.  Marr,  M.A., 
F.R.S.,  Sec.G.S.,  from  notes  made  by  the  late  Mr.  Thomas  Roberts, 
M.A.,  F.G.S.  The  value  of  the  work  is  guaranteed  by  the  fact  that 
so  competent  an  authority  as  Mr.  Marr  has  thought  it  desirable  to 
place  Mr.  Roberts’s  observations  on  record,  and  has  given  much  of 
his  valuable  time  to  the  verification  of  the  facts  and  the  arrangement 
of  the  notes  in  a  form  suitable  for  communication  to  this  Society. 
T.  McKenhy  Hughes. 
In  a  paper  published  in  the  Society’s  Journal  in  the  year  1885  1 
a  complex  synclinal  of  Lower  Palseozoic  rocks  occurring  in  the  neigh¬ 
bourhood  of  Haverfordwest  was  described.  Owing  to  the  occurrence 
of  a  fault  at  the  northern  side  of  that  synclinal,  no  strata  of  Arenig 
age  were  noticed  in  the  paper,  the  oldest  Ordovician  beds  refened 
to  being  the  Tidymograptus  3Iurchisoni-shales  below  the  Llandeilo 
Limestone  in  the  neighbourhood  of  Narberth,  at  the  south-eastern 
end  of  the  synclinal.  It  seemed  important,  therefore,  to  work  the 
strata  lying  east  of  Narberth  in  order  to  try  and  discover  Arenig 
Beds  in  the  district  between  that  town  and  Caermarthen.  This  was 
accordingly  done  in  some  of  the  vacations  between  1886  and  1890, 
and  a  complex  anticlinal  was  discovered  lying  north-east  of  the 
Haverfordwest  synclinal,  having  its  oldest  beds  exposed  north,  of 
Whitland.  The  accompanying  map  shows  the  general  distribution 
of  the  beds  in  this  anticlinal,  no  attempt  being  made  to  trace 
accurate  boundary-lines ;  but  two  approximate  boundaries  are  drawn 
at  the  top  of  the  Tetragraptns- beds  (to  be  presently  described)  and 
along  the  line  of  outcrop  of  the  Llandeilo  Limestone  respectively,  in 
order  to  show  the  general  distribution  of  the  strata  and  the  nature 
and  direction  of  the  anticlinal.  The  beds  may  be  described,  in 
ascending  order,.,  as  follows  : — 
1.  Tetragraptns- beds. — These  beds  consist  of  alternating'  con¬ 
glomerates,  shales,  and  grits,  seen  at  Talfan,  Pen-parc-uchaf,  and 
probably  near  Whitland  Abbey,  all  places  lying  generally  north  of 
Whitland.  The  shales  have  yielded  graptolites,  kindly  determined 
by  Prof.  Lapworth,  as  follows  : — 
Dictyonema  .  North  of  Talfan. 
Dendrogaptus,  sp .  Ibid. 
Didymograptus  nitidus,  Hall . . .  Ibid. 
- patulus,  Hall  .  North  of  Talfan  and  Pen-parc-uchaf. 
Tetragraptns  Headi ,  Hall  .  North  of  Talfan. 
- serra,  Brougn.  . .  Ibid. 
Callograptus  Salteri,  Hall  .  Ibid. 
- persculptus  .  Ibid. 
Dichograptid  .  Ibid. 
1  Marr  and  Roberts,  Quart.  Journ.  Geol.  Soc.  vol.  xli.  p.  476. 
