506 SILUDIES FOR STUDENTS 
interior epicontinental sea of Devonian time in eastern North 
America was relatively sudden. 
Such a sudden appearance, in a series of sedimentary rocks, 
of a new fossil fauna, with apparently no genetic predecessors in 
the immediate region, may be compared with the sudden appear- 
ance in North America during the sixteenth century of the 
advanced culture and civilization of Europe among the savage 
tribes which had occupied the continent previous to that time. 
Although the appearance in America of the white man with his 
advanced culture was sudden, and his influence spread so rapidly 
that it soon drove into practical extinction the preéxisting and 
less advanced culture of the Indian, it was really the culmination 
of a long and gradual development, in Europe, of the art of 
building and sailing ships. Ina similar way the sudden appear- 
ance of a new fossil fauna in a series of sedimentary rocks may 
be but the culmination of some physical change which has been 
in progress during an extended period of time. The submerg- 
ance or the erosion of a land mass may be slow, and may con- 
tinue through a long lapse of time, but the culmination of the 
phenomenon will be when the land passes below sea level, thus 
removing a barrier and allowing the immigration of a marine fauna 
into a region previously occupied by a very different assemblage 
of organisms. The conflict following such an immigration may 
be compared with the conflict between the Indian and the Euro- 
pean cultures in America. 
The resulting fauna from any such incursion and mingling 
within an interior sea, as has been described above, will of course 
be different from either of the original faunas. The Corniferous 
fauna in eastern North America, in addition to that element 
which came in from the outside, contains also an element which 
may be traced directly back to the preceding Oriskany or Hel- 
derberg faunas which had inhabited the same region. When the 
German tribes made their incursions into the Roman Empire, 
bringing in a new culture, the old Roman civilization and culture 
was not entirely destroyed, but there was built up a new civiliza- 
tion and a new culture, differing from either the Roman or the 
