488 THE JOURNAL OF GEOLOGY. 
rence was described by the writer’ and by Professor H. S. Wil- 
liams? in the Fayetteville Shale, Lower Carboniferous, of Arkan- 
sas. A survival of a Devonian fauna in rocks of Lower Carbon- 
iferous age has been described from Nevada by Professor C. D. 
Walcott,3 and from California by the writer.‘ 
It is becoming more evident all the time that the range of 
faunas, instead of being usually the same in widely separated 
regions, is usually different, and that strata can no longer be 
called synchronous from the occurrence in them of similar faunas. 
In reality they can no longer be called homotaxial with any 
degree of certainty, unless we know in what direction the faunas 
migrated, since homotaxis in the paleontologic sense does not 
agree with homotaxis in the stratigraphic sense. 
The extensive extinction of life at one place earlier than 
in another has also been noted. Professor W. Waagen®’ has 
suggested that the glaciation in the southern hemisphere toward 
the end of the Carboniferous killed off the Paleozoic flora earlier 
than was the case in regions where there was no glaciation. 
Such phenomena approach the nature of ‘catastrophes,’ and 
show that Cuvier’s doctrine was not so far wrong after all. 
The study of the distribution of faunas in the past seems to 
show that their extinction has been chiefly due to changes in 
physical geography; and that where conditions remained con- 
stant the faunas remained unchanged. This study too suggests 
that no part of the earth has remained unchanged, for while some 
of the abysmal regions may be very old, even their faunas are of 
comparatively modern aspect. 
MEANS OF MIGRATION.® 
Few invertebrates are rapid swimmers. Many are attached 
forms and the majority are only crawlers. But all are free at 
tJour. GEOL., Vol. IL, p. 198. 
2Am. Jour. Sci., III. Ser. Vol. 49, pp. 94-101. 
3 Monograph VIII. U. S. Geol. Survey. 
4Jour. GEOL., Vol. II., p. 595. 
5 Pal. Indica. Salt Range Fossils. Geol. Results, p. 240. 
© Accidental distribution need not be considered here; it may have occurred, but 
must have been very rare. 
