In  Scotland  fishes  are  more  or  less  found  in  all  the
broader  districts  occupied  by  Old  Red  Sandstone,  but  it
was  chiefly  in  the  north,  in  Caithness,  and  on  both  sides
of  Cromarty  and  Moray  Firths,  that  Hugh  Miller  made
his  wonderful  discoveries  of  fossil  fishes  of  many
species.  They  are  found  generally  in  bituminous
schists  and  flags  with  occasional  nodular  concretions,
and  lie  in  various  minor  horizons  among  red  and  varie-
gated sandstones  and  conglomerates,  which  contain  the
remains  of  many  fish  of  the  genera  Diplopterus,
Coccosteus-)  PterichikyS)  Diplacanthus,  Osteolepis,
Glyptoloemus,  Dipterus,  Holoptychius,  Cephalaspis,
besides  Crustacea,  such  as  Pterygotus9  and  the  small
bivalve  Estheria  Murchisonice.  (Fig.  26.)

Most  of  the  genera  belong  to  a  sub-order  of  Ganoid
fish  called  Crossopterygidce  by  Huxley,  from  the  fringe-
like  arrangement  of  the  fins,  a  sub-order  several  species
of  which  are  still  living  in  the  rivers  of  Senegal  and  in
the  Nile.
I  have  specially  mentioned  these  circumstances,  for
the  purpose  of  keeping  before  the  mind  of  the  reader
the  broad  fact  that  the  Old  Red  Sandstone,  as  a  whole,  is

I


FIG.  26.
Pterygotus  Anglicus.  Cephalaspis  Lyelii.
Group  of  Old  Red  Sandstone  fossils.
