36 
THE SILURIAN BEACH. 
ning of organic life, the less marked clo we find 
the differences to be, and for a very obvious rea- 
son. The inequalities of the earth’s surface, her 
mountain-barriers protecting whole continents 
from the Arctic winds, her open plains exposing 
others to the full force of the polar blasts, her 
snug valleys and her lofty heights, her table- 
lands and rolling prairies, her river-systems and 
her dry deserts, her cold ocean-currents pouring 
down from the high North on some of her shores, 
while warm ones from tropical seas carry their 
softer influence to others, — in short, all the con- 
trasts in the external configuration of the globe, 
with the physical conditions attendant upon 
them, are naturally accompanied by a corre- 
sponding variety in animal and vegetable life. 
But in the Silurian age, when there were no 
elevations higher than the Canadian hills, when 
water covered the face of the earth, with the ex- 
ception of a few isolated portions lifted above the 
almost universal ocean, how monotonous must 
have been the conditions of life ! And what 
should we expect to find on those first shores ? 
If we are walking on a sea-beach to-day, we do 
not look for animals that haunt the forests or roam 
over the open plains, or for those that live in shel- 
tered valleys or in inland regions or on mountain- 
heights. We look for Shells, for Mussels and 
Barnacles, for Crabs, for Shrimps, for Marine 
