ARCHEAN AND PALEOZOIC LIFE 407 
condition of schists, and even of gneisses, which closely resemble 
the rocks of the Archean. In fact, because of this resemblance, 
the strata of many parts of New England were for a long time 
classified as Archean, though they are now known to have been 
formed as sediments in the Paleozoic ocean. 
The sedimentary beds of the more recent ages, more and more 
nearly approach the condition of the strata that are now being 
deposited in the ocean. Indeed, as a general statement it may be 
said, that the strata of the later ages are less and less solidified. 
There is every gradation between the extremely dense and hard 
sandstone of the early Paleozoic time, and the unsolidified sand of 
the modern beach. 
Cambrian Organisms. — Something of the same sort as 
that just described for the Archean, applies to the Cam- 
brian, the first of the Paleozoic ages. These rocks, the 
most ancient of the sedimentary strata, have been most 
subjected to changes; and hence many fossils that were 
originally preserved in them have in large measure been 
destroyed. Notwithstanding this, the Cambrian strata 
have furnished us with many different species of ani- 
mals. It is possible that some plants and animals may 
have dwelt upon the land, but if so, they have failed 
to leave us a record of their existence. 
Seaweeds are the only plants found fossil in the 
Cambrian rocks. The animals are all invertebrates, but 
not of extremely low forms. Corals, not unlike those 
of the present, lived in great numbers; and shell-fish, 
similar to some forms still existing, crawled over the 
ocean bed or burrowed in the mud. The two most 
