THE SILURIAN BEACH. 
61 
crowded with life, and its last leaves as full and 
varied as its first. 
I think the impression that the faunae of the 
early geological periods were more scanty than 
those of later times arises partly from the fact 
that the present creation is made a standard 
of comparison for all preceding creations. Of 
course, the collections of living types in any 
museum must be more numerous than those of 
fossil forms, for the simple reason that almost 
the whole of the present surface of the earth, 
with the animals and plants inhabiting it, is 
known to us, whereas the deposits of the Silurian 
and Devonian periods are exposed to view only 
over comparatively limited tracts and in discon- 
nected regions. But let us compare a given ex- 
tent of Silurian or Devonian sea-shore with an 
equal extent of sea-shore belonging to our own 
time, and we shall soon be convinced that the 
one is as populous as the other. On the New- 
England coast there are about one hundred and 
fifty different kinds of fishes, in the Gulf of Mex- 
ico two hundred and fifty, in the Bed Sea about 
the same. We may allow in present times an 
average of two hundred or two hundred and fifty 
different kinds of fishes to an extent of ocean 
covering about four hundred miles. Now I have 
made a special study of the Devonian rocks of 
Northern Europe, in the Baltic and along the 
