I have spoken of the Silurian beach as if there were but one, not only because I wished to limit my sketch, and to attempt at least to give it the vividness of a special locality, but also because a single such shore will give us as good an idea of the characteristic fauna of the time as if we drew our material from a wider range.  There are, however, a great number of parallel ridges belonging to the Silurian and Devonian periods, running from east to west, not only through the State of New York, but far beyond, through the States of Michigan and Wisconsin into Minnesota; one may follow nine or ten such successive shores in unbroken lines, from the neighborhood of Lake Champlain to the Far West.  They have all the irregularities of modern sea-shores, running up to form little bays here, and jutting out in promontories there; and upon each one are found animals of the same kind, but differing in species from those of the preceding.

Although the early geological periods are more legible in North America, because they are exposed over such extensive tracts of land, yet they have been studied in many other parts of the globe.  In Norway, in Germany, in France, in Russia, in Siberia, in Kamtchatka, in parts of South America, in short, wherever the civilization of the white race has extended, Silurian deposits have been observed, and everywhere they bear the same testimony to a profuse and varied creation.  The earth was teeming then with life as now, and in whatever corner of its surface the geologist finds the old strata, they hold a dead fauna as numerous as that which lives and moves above it.  Nor do we find that there was any gradual increase or decrease of any organic forms at the beginning and close of the successive periods.  On the contrary, the opening scenes of every chapter in the world’s history have been 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 disconnected regions.  But let us compare a given extent 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 Mexico two hundred and fifty, in the Red Sea about the same.  We may allow in present times an average of two hundred or two hundred and fifty different kinds of fishes