John Allen Howe

“ The three broad divisions—Palaeozoic, Mesozoic, Cainozoic—which are employed by geologists to mark three stages in the development of life on the earth, are based primarily upon the fossil contents of the strata which, at one time or another, have been continuously forming since the earliest times. ”

“ The divisions in the fossil record having been thus established, they must for convenience remain, but their artificially cannot be too strongly emphasized, for the broad stratigraphical gaps and lithological groups which made the divisions sharp and clear to the earlier geologists are proved to be absent in other regions, and fossils which were formerly deemed characteristic of the Palaeozoic era are found in some places to commingle with forms of strongly marked Mesozoic type. ”

“ Cambrian, Ordovician, Silurian, Devonian, Carboniferous and Permian. The fact that fossils found in the rocks of the three earlier epochs—Cambrian, Ordovician, Silurian—have features in common, as distinguished from those in the three later epochs has led certain authors to divide this era into an earlier, Protozoic (Proterozoic) and a later Deuterozoic time. The rocks of Palaeozoic age are mainly sandy and muddy sediments with a considerable development of limestone in places. ”