438 
MESSES.  P.  LAKE  AND  T.  T.  GROOM  ON  THE 
[Aug.  1893, 
much  better  preserved.  Near  the  foot  of  the  first  waterfall  we 
found  a  band  made  up  almost  entirely  of  graptolites.  The  species 
found  here  (also  determined  by  Mr.  I.  E.  Marr)  are : — 
Monograptus  convolutus ,  His.  (abun¬ 
dant). 
- leptotheca,  Lapw. 
• - Nicoli,  Harkn. 
- -  te?iuis ,  Portl. 
Monograptus  jhnbriatus  ?  Nick. 
Diplograptas  tamariscus,  Nicb. 
- sinuatas,  Nich.  (very  abundant). 
Petalograptus  ovatas  ?  Barr. 
Climacograptus  normalis,  Lapw. 
On  the  western  side  of  this  fault  the  grey  slates  with  grit-bands 
are,  as  already  described,  followed  by  black  shales  in  which  one 
or  two  unrecognizable  graptolites  were  found  ;  these  are  again 
followed  by  bluish  slates,  and  these  by  banded  black  shales.  I11 
the  latter  we  found  M.  convolutus  and  one  or  two  other  forms, 
and  they  evidently  correspond  with  the  graptolite-shales  just 
mentioned. 
All  these  graptolites  belong  to  the  conpohukts-subdivision  of  the 
gree/arius- zone — the  upper  zone  of  the  Lower  Birkhill — and  it  is 
clear  therefore  that  these  shales  are  of  Lower  Birkhill  age. 
(e)  Pale  Slates. — In  Naut  Cawrddu  the  graptolite-shales  of  the 
new  reservoir  are  succeeded  by  pale  bluish  slates,  which  extend  as 
far  as  the  Corwen  Fault. 
In  Nant  Llechog  the  graptolite-shales  are  followed  by  somewhat 
lighter-coloured  beds  ;  and  in  the  hill  just  above  old  workings  have 
thrown  out  pale  slates,  such  as  frequently  lie  immediately  below  the 
Tarannons  in  this  area.  But  tho  whole  of  the  rocks  between  the 
gregarius- shales  and  the  slates  of  Pen-y-glog  (Denbighshire  Slates) 
are  covered  by  drift,  and  no  section  in  this  area  exposes  the  higher 
beds  of  the  Llandovery  Series. 
Y.  List  of  Fossils  found  at  and  near  Corwen. 
Lepteena  sericea,  Sow. 
Ortkis  elegantula,  Balm. 
Corwen. 
Grey  Slates. 
Bhynchonella : 
Calymene  Blumenbachii,  Brongn. 
Beds  immediately  below  the  Corwen  Grit. 
Lepteena  sericea,  Sow.  (abundant). 
Ortkis  elegantula ,  Dalm.  (abundant). 
- testudinaria,  Dalm. 
- culligramma,  Dalm. 
- biforata,  Schlotk. 
- porcata ,  M‘Cov. 
IStrophomena  rkomboidalis,  Wilck. 
- simulans,  M‘Coy. 
Lingula,  ovata,  var. 
Orthoceras  ibex,  Sow. 
Conularia  Sowerbyi,  Defr. 
Phyllopora  Hidngeri,  M‘Coy. 
Ptilodictya  sp. 
Pinnatopora  Sedgwicki  ?  Shrubs. 
lUcenus  Bowmanni,  Salt. 
Oinoids  (abundant). 
Favosites  fibrosa,  Goldf.,  and  other 
Favositids  (abundant). 
