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156 GEOLOGY. 
consists of minute tubes or cells that are visible only under the micro- 
scope. Some still deny that this structure is organic, and regard it as 
merely a mineral appearance ; but these are few. The general opinion 
now is that here we have the earliest life-remains yet discovered on our 
globe ; and this all the more certainly that worm tracks and burrows were 
found in 1866 in the same formation. The discovery of these evidences 
of organic life, so long sought in vain, shews that more minute search may 
result in other remarkable discoveries, and that in all likelihood the name 
of Eozdon will be found to be premature. 
IiI.—Cambrian System. 
Description.—Immediately above the Laurentian lies a series of slates, 
schists, and crystalline limestones, called the Cambrian System. It is so” 
named from being first most fully described as it is found in North 
Wales, which in Roman times was called Cambria. The rocks in this 
series are less changed than the Laurentian, and therefore the remains in 
them are more numerous and better preserved. They are of great thick- 
ness, and are found in Wales, Cumberland, North-west Scotland, Ireland, 
North America, and elsewhere. Along with the older rocks beneath 
them, they everywhere form mighty rugged peaked mountains, like those 
of Wales and the Highlands ; and their worn rugged aspect is due to their 
being so long subjected to wasting influences from their great antiquity. 
All these earlier rock-formations, from the Metamorphic to the Silurian, 
are exceedingly rich in mineral wealth, most of the precious metals being 
obtained from them. Shooting through their hard crystalline masses, we 
find veins of iron, copper, silver, and gold; and, from the presence of 
these metals, bare mountain tracts have teeming populations, where even 
the sheep with difficulty finds its scanty food. 
Organic Remains.—The fossil remains are all of the very lowest kinds 
of life. Sea-weeds, shells of different kinds, and some crustacea, especially 
one that occurs abundantly in the next formation, called the trilobite, 
have been discovered. The tracks and burrows of worms, formed in the 
sand of the ancient seas, may also be seen perforating these hard masses. 
Scenery of Period.—During the Cambrian age, quiet seas heaved their 
waters as now, tenanted with shells and crab-like creatures, while waves 
rolled on the sandy shores, over which worms crawled, and into which 
they burrowed ; interesting as shewing that creatures had then the same 
kinds of habits as now, and that what we can see any day along our own 
shores sends us back to the distant ages when the world was young! 
