488 Dr. H. Trautschold—FPeriodical Movement of the Ocean. 
and the Trias on one side, and the Chalk sea and the Eocene period 
on the other, there is a greater difference than between the animal 
world of any of the other periods. In the transition-period between 
Permian and Trias, Corals, Cephalopods, Reptiles, etc., under- 
went an astonishing change; thousands of forms seemed to have 
perished, thousands of new ones appeared; in the succeeding time, 
shortly after the commencement the fauna of the Mesozoic seas 
showed, on the whole, quite another stamp, than that of the Palao- 
zoic seas. A quite undisturbed development seemed to have reigned 
from Silurian to Permian, and there seemed to have been a sudden 
interruption of that development during the Permian period. Again, 
there followed an era of the most quiet and peaceful evolution during 
the Triassic, Oolitic and Cretaceous periods, where the connection 
between the several marine faunas seems to have been an uninter- 
rupted one; then, at the end of the Cretaceous period, the marine 
fauna underwent a new change. The dawn of a new time (Hocene) 
begins, thousands of forms again disappear to be replaced a second 
time by new ones, as had occurred during the Permian period. Again, 
the Cephalopods seem to have been the class against which a war 
of annihilation was directed, and in their place the Pelecypods and 
Gasteropods take the leadership in the new era. The Enaliosaurians 
having reached a high development die out entirely and the Croco- 
dilians retire to the rivers. The Secondary fauna gives way to the 
Tertiary, bearing a thoroughly new stamp. 
What was the cause of such an important change in the first as 
well as the second instance? Geology is by far too new a science 
to solve important questions like these. Notwithstanding the mar- 
vellous zeal with which the surface of the earth has been explored 
in our century, larger spaces of it can only be opened to our know- 
ledge after the lapse of a great many years, and therefore it is quite 
impossible at once to draw general conclusions from the results of 
these investigations. But now, Europe having been explored in 
the most careful manner, as well as the structure of the North- 
American continent to a great extent, now that Russian naturalists 
and v. Richthofen have made us more familiar with the Asiatic 
continent, we may venture to open out more general views. Now we 
are able to answer the question with more assurance, what was the 
cause of the apparent interruption in the evolution of the maritime 
fauna at the end of the Permian and the beginning of the Tertiary 
periods in the northern hemisphere ? 
The cause of these phenomena was no other than the periodical 
movement of the ocean. 
The most suitable areas for the clear demonstration of this move- 
ment are large plains, built up by horizontal strata, whose order 
has never been disturbed. A plain of this kind is to be found in 
European Russia. It leaves nothing to be desired as to the un- 
disturbed horizontality of its strata, and the surface shows in the 
direction of its rivers only a slight inclination towards the south and 
south-east. A glance over the map of Murchison and Helmersen 
makes it evident that in the north of European Russia the Paleozoic 
