YoL  49. j 
COXGIOUZEAIZS  IX  CASBjSTAEVOXSHIRE. 
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we  correlated  them  with  c  they  should  be  followed  by  the  Banded 
Slates,  which  is  not  the  case.  A  third  example  is  above  23,  where 
we  find  conglomerate  Ivina:  on  the  surface  of  Pale  Slates. 
Big.  4. — H<yriz:  it  .  Bn  ed  Grits  over  Bode  Slates. 
w. 
It  is  not.  however,  always  easy  in  particular  spots  to  distinguish 
the  beds  which  for  the  above  reasons  I  refer  to  a  later  date,  for  they 
are  a  curious  mixture,  very  inconstant  in  some  respects.  But  when 
one  gets  familiar  with  them,  the  irregular  stratification  in  crinkly 
lines,  the  apparent  false  bedding,  and  the  mottled  colour  due  to 
the  intermixture  of  various  detritus  appear  very  characteristic ; 
although  vrhere  one  or  other  material  preponderates  the  result  may 
be  more  or  less  mimetic  of  the  rocks  from  which  the  detritus  has 
been  derived. 
My  general  notion  of  the  structure  of  Y  Bigl.  after  eliminating 
contortions,  is  represented  in  fig.  5.  where  the  post-Llanberis  beds 
a  —  I  el  die.  5  —  Cambrian  Beds. 
c.  d  —  Post-Llanberis  Conglomerates  and  Grits. 
[Horizontal  Scale:  10  inches  =  1  mile.] 
may  possibly  he  represented  too  thick.  At  all  events,  we  have  the 
following  broad  facts  to  go  upon.  Over  the  centre  of  a  synclinal  we 
have  a  vast  continuous  mass  of  conglomerates  and  grits  rising  to  a 
height  of  30 U  feet  above  the  main  exposures  of  the  slates,  while  we 
find  these  slates  in  the  low  ground  on  either  side  to  the  north  and 
south  along  the  line  of  their  strike  :  and  while  in  no  locality  can  we 
find  the  former  underhung  the  latter,  in  several  localities  we  find 
them  actually  overhung.  It  is  true  that  we  do  not  here  see  the 
conglomerates  transgressing  over  the  Purple  Slates,  unless  the 
approximation  of  3  and  4  is  a  natural  one ;  but  they  do  so  in  the 
area  next  to  be  described. 
A  further  argument  for  their  unconformity — and  indeed  the  one 
which  original iv  led  me  to  believe  that  there  was  something  wrong 
in  the  accepted  explanation — is  afforded  by  Moel  Goronwy.  On  the 
