A CENTURY OF PROGRESS IN PALEONTOLOGY 505 
geographic limits of the provinces themselves. The major 
development of the several great Devonian provinces was, in all 
probability, in shallow seas upon the borders of the continents, 
and the more important changes in their areal distribution was 
probably due to the cutting away of barriers formed by the more 
or less elevated rim of the continents, and the extension of lobes 
of the sea into the interior, so forming interior epicontinental 
seas. It is in the sediments of these interior epicontinental 
seas that the greater portion of all our Paleozoic life records 
are preserved. The borders of the continents are the chief 
regions of disturbance during periods of dynamic activity, 
so that the records of the life in the normal border prov- 
inces of such a period as the Devonian are to a great extent 
destroyed. 
If we were able to possess ourselves of sufficient data in 
regard to the border provinces, it is probable that no sharp life 
breaks would be found, but in the interior epicontinental seas, 
the case is very different. By the slow cutting away by erosion 
of the barrier rim, or by the local sinking of the land, communi- 
cation is established successively between the interior seas, and 
first one and then another of the great border provinces, and 
there are successive incursions of very different faunas, which 
make their appearance in the interior very suddenly, although 
their evolution has been in progress in some border province 
during a long lapse of time. As an illustration of such a sudden 
appearance of a fauna into an interior epicontinental sea, the 
fauna of the Corniferous in eastern North America may be 
mentioned. This fauna with its large number and variety of 
corals, its great number of cephalopods including the first goniatite, 
and, most of all, the host of armored fishes, appears with com- 
parative suddenness, probably from the north through Hudson 
Bay, and includes many organisms which could not possibly have 
been derived from the preceding Devonian faunas, the Oriskany 
and Helderberg. The evolution of this fauna had probably been 
in progress during all the preceeding time since the Silurian in 
its more or less isolated province, but its appearance in the 
