SOURCE OF EVOLUTION OF PROVINCIAL FAUNAS 607 
fauna. It was followed in succession by the invasion of the 
Oriskany fauna, whose place of origin is less clear, but which 
followed the Helderberg track; by the Corniferous fauna, appar- 
ently from the Hudson’s Bay embayment; by the early Hamil- 
ton fauna, apparently from some southern embayment; and by 
the later Hamilton fauna,apparently from the Mackenzie embay- 
ment, or beyond, thus giving to the Devonian period a distinctive 
aspect as a time of successive invasions of provincial faunas gen- 
erated in embayments about the borders of the continent.t. Had 
the waters been withdrawn so far as to have emptied these 
embayments, as was apparently the case at the close of the 
Paleozoic era, a general repressional evolution would have taken 
the place of this pronounced provincial evolution. The deter- 
minative element, therefore, seems to have been (the critical atti- 
tude of the sea to the land which gave maximum effect to the 
inequalities of its border. 
It is obvious that any previous warping of the continental 
platform by which a portion of it is submerged may give rise to 
an embayment covered by relatively shallow water at times of 
the ocean’s withdrawal, and that this may become a refuge for 
the retreating faunas, and may break the force of the general 
repressional evolution which would otherwise ensue. This may 
take place even when the seas are withdrawn down to a level 
much below the critical horizon just discussed. Such embay- 
ments may be regarded as adventitious, since they are not the 
product of the systematic actions here discussed. But such 
adventitious embayments were probably always present at times 
of great withdrawals of the sea, and so broke the force of repres- 
sional evolution. Inthe withdrawal of the sea at the close of the 
Paleozoic era, the Mediterranean basin appears to have afforded 
such a retreat for the hard-pressed Permian life of the western 
part of the Eurasian continent, and to have become a transitional 
tract in which originated one of the three or four great provincial 
faunas that advanced upon the land in the Triassic and Jurassic 
periods. A similar great embayment appears to have existed in 
? Drawn mainly from the studies of H. S. Williams and Stuart Weller. 
