42 
THE SILURIAN BEACH. 
The scales of the oldest known fishes in the Silu- 
rian beds have the same microscopic structure as 
those of their representative types to-day, and yet 
[ have never seen a single fossil fish presenting 
the same specific characters in the successive geo- 
logical epochs. The teeth of the oldest Sharks 
show the same microscopic structure as those of 
the present time, and we do not lack opportuni- 
ties for comparison, since the former are as com- 
mon in the mountain-limestone of Ireland as are 
those of the living Sharks on any beach where 
our fishermen boil them for the sake of their oil, 
and yet the Sharks appear under different generic 
and specific forms in each geological age. 
But without multiplying examples, which 
might be adduced, ad infinitum , to show perma- 
nence of type combined with repeated changes 
of species, suffice it to say, that, while the gen- 
eral features in the framework of the organic 
world and the materials of which that framework 
is built, though quite as subject to the influence 
of physical external circumstances as any so- 
called specific features, have remained perfectly 
intact from the beginning of Creation till now, 
so that not the smallest difference is to be dis- 
cerned in these respects between the oldest repre- 
sentatives of the oldest types in the oldest Silu 
rian rocks and their successors through all the 
geological ages up to the present day, the species 
