GRADATION AMONG ANIMALS. 93 
the investigation of this succession, because, in 
consequence of its mode of formation, we have, 
in the State of New York, a direct, unbroken se- 
quence of all the earliest geological deposits. 
The ridge of low hills, called the Laurentian 
’ Hills, along the line of division between Canada 
and the States was the first American land lifted 
above the ocean. That land belongs to the Azoic 
period, and contains no trace of life. Along the 
base of that range of hills lie the deposits of the 
next great geological period, the Silurian ; and 
the State of New York, geologically speaking, 
belongs almost entirely to this Silurian period, 
with its lowest Taconic division, and the Devon- 
ian period, the third in succession of these great 
epochs. I need hardly remind those of my read- 
ers who have travelled through New York, and 
have visited Niagara or Trenton, or, indeed, any 
of the localities where the broken edges of the 
strata expose the buried life within them, how 
numerous this early population of the earth must 
have been. No one who has held in his hand one 
of the crowded slabs of sandstone or limestone, 
or slate full of Crustacea, Shells, and Corals, 
from any of the old Silurian or Devonian beaches 
which follow each other from north to south 
across the State of New York, can suppose that 
the manifestation of life was less multitudinous 
then than now. 
