THE NATURALISTS’ COMPANION, 
89 
Huronian and Lacrentine. 
The ArchcTean surface rocks of 
North America comprise a V shap¬ 
ed region, running from the Arctic 
Ocean on the north-west to the great 
lakes, and then north-east to Lab¬ 
rador. This V shaped region was 
the first dry land of the continent. 
The rocks of the Archman Time 
are mostly crystalline or metamor- 
phic, and comprises granite, gneiss, 
marble, cpiartzite, syenite, lime¬ 
stone, etc. Beds of graphite, por- 
phy, soapstone and slates are found. 
This was the age of iron making. 
The earlier part of the Archaean 
Time was of course without life of 
any kind. But as soon as the 
earth was cool enough, life began 
to appear. The first organisms 
were very simple, such as seaweeds, 
etc. 
CHAPTER II. 
PALEOZOSC TiME. 
The Paleozoic time is divided in¬ 
to three ages, namely : The Siluri¬ 
an or age of mollusks, the Devon¬ 
ian or age of fishes, and the Car¬ 
boniferous or age of coal-plants. 
I-SSLUR!A['J AGE. 
The name Silurian comes from a 
region in Wales, where the rocks 
are found, and which had been for¬ 
merly inhabited by a tribe ol Brit¬ 
ons, called Silures. 
This was the first grand act on 
the stage of life. 
The Silurian age is subdivided 
as follows: 
4 Oriskany Period. 
§ 3 LowerHelderbergP’d 
SILURIAnI " syua Period. 
^ I Niagara Period. 
p; 3 Hudson Period. 
2 Trenton Period. 
5 • Potsdam Period. 
Probably at this time the Appal¬ 
achians and the Rocky Mountains 
were already towering out from the 
sea. The land was mostly low 
and rocky, and the shallow waters 
were filled with mollusks and crus¬ 
taceans. The sun shown pale and 
dim through the dense atmosphere, 
throwing an uncertain light over 
the scene. 
The first period of this age is the 
POTSDASVi PERIOD. 
This period is named from a town 
in northern New York by that name. 
The formation is found in Pennsyl¬ 
vania and westward through Michi¬ 
gan, along Lake Superior, through 
Wisconsin and Minnesota, to the 
Black Hills of Dakota. It runs 
so’thward from Vermont to Alabama 
along the Appalachian range. It 
is also found in Texas. The rock 
varies indifferent places. At some 
places being a coarse,hard sandstone 
and in others a fine white sand. In 
many places these rocks are found 
worm-burrowed and marked with 
ripples and mud-cracks. They are 
also often found with marks and 
tracks of the animals of that time. 
This shows they were not made in 
deep water,but on a low sand-beach 
or mud-flat ; and that part of the 
time they were above the water,and 
exposed to the sun. 
The trilobite, a crustacean, is the 
most conspicuous and inter¬ 
esting fossil of this period, and also 
of the whole Silurian age. It has 
been found almost perfectly pre¬ 
served. It had an oval figure, and 
was covered wdth a jointed crust. 
No legs have ever been found with 
trilobites ; they are supposed to 
have had only a kind of thin mem¬ 
braneous plates, for swimming. 
A small shell called is 
