446 
REV.  J.  E.  DRAKE  ON  EELSITES  AND 
[Aug.  1893, 
Purple  Slate,  to  which  latter  nothing  between  b  and  e  corresponds. 
It  seems  to  me  that  this  sudden  change  proves  that  there  is  no 
anticlinal,  but  a  fault  somewhere  between  h  and  &,  in  which  case 
the  conglomerate  i  may  be  let  down  in  the  trough.  When  seen  in 
contact  with  Jc  the  relations  are  not  certain  ;  it  partly  appears  to 
interosculate,  aud  partly  to  have  a  different  direction  of  bedding  and 
to  be  slickensided  ;  we  must  therefore  leave  it  undecided  whether 
this  band  lies  naturally  below  the  grit  h  or  is  faulted  against  it. 
P)ut  the  main  point  in  this  section  has  been  left  as  yet  unnoticed 
— the  occurrence  of  another  conglomerate  of  large  stones  lying  on  the 
top  of  the  peculiar  breccia  (g).  These  two  had  been  confounded  with 
each  other  till  Prof.  A.  H.  Green  described  their  unconformity.1  His 
account  of  the  general  section  agrees  very  closely  with  the  above, 
while  his  description  of  the  relations  of  the  unconformable  conglo¬ 
merate  (A)  to  the  beds  below  ( g  and  h),  and  of  the  characters  of  each, 
is  so  wonderfully  true  to  nature  that  I  can  only  quote  him  verbatim 
from  the  words  4  the  first  rock’  (op.  cit.  p.  74)  to  4  their  character ' 
(p.  77),  and  I  must  demur  entirely  to  the  words  of  the  President 
(Prof.  Ponney)  on  that  occasion,  that  ‘the  section  is  not  so  clear  in 
nature  as  in  the  diagram.’  The  apparent  unconformity  is  considered, 
however,  by  Sir  Archibald  Geikie  to  be  due  to  the  cleavage  of  the 
4  fine  tuffs,’  as  he  designates  the  breccias,  and  the  non-cleavage  of  the 
conglomerate.  The  urger  of  this  objection  at  least  recognizes  the 
difference  between  the  two,  which  others  have  failed  to  do ;  but 
neither  Prof.  Green’s  reasoning  nor  my  own  has  any  connexion  with 
the  cleavage  or  otherwise  ;  it  is  that  a  conglomerate  lies  in  nearly 
,  horizontal  beds,  or  at  least  with  a  nearly  horizontal  line  of  separation, 
upon  a  mass  of  another  rock,  different  vertical  sheets  of  which  have 
different  characters.  I  cannot  imagine  a  more  satisfactory  proof 
of  unconformity  in  a  single  section. 
Nevertheless,  were  this  section  only  studied  and  the  unconformity 
admitted,  the  most  natural  suggestion  would  be  that  made  by 
Prof.  Hughes  in  the  discussion  on  Prof.  Green’s  paper,  that  the  beds 
r/,  li  belong  to  an  older  series  than  the  beds  a-f  (including  therein 
the  unconformable  A).  It  is  when  we  follow  the  beds  over  the 
surface  of  the  country  that  the  difficulties  begin.  The  accompanying 
map  (p.  447),  in  which  several  minor  details  are  omitted,  will  enable 
the  argument  to  be  followed. 
The  first  difficulty  in  the  old  interpretation  is  connected  with  the 
eastern  boundary  of  the  conglomerates,  etc.  At  19,  24  we  find  them 
to  the  east  of  the  felsite ;  a  little  farther  north  they  are  close  to  the 
Purple  Slate  at  3,  4 ;  and  at  5,  6  there  is  none  between  the  felsite 
and  the  slate.  This  difficulty,  however,  may  be  due  to  a  fault  sug¬ 
gested  by  the  section  in  the  railway,  though  not  introduced  into  the 
map.  The  main  difficulty  is  the  supposition  that  the  conglomerates 
(a,  A,  etc.)  underlie  the  mass  of  banded  slates,  etc.  (b-e).  The  non¬ 
correspondence  of  the  sequence  at  A,  g,  h — 2,  7  in  the  section — with 
that  at  a  (8,  9)  on  the  opposite  side  of  the  synclinal  cannot, 
be  accounted  for  by  a  fault  between  a  and  y,  as  suggested  by 
1  Quart.  Journ.  Geol.  Soc.  vol.  xli.  (1885)  p.  74. 
