THE PALEONTOLOGIC RECORD 71 
the arrival of the Chemung fauna; and in western New York no trace 
of the Catskill type of sediments appears till after the close of the 
Devonian. 
These facts are direct evidence of shifting of the environmental 
conditions of the edge of the continent westward as the deposits of the 
middle and upper Devonian were being laid down. With this shifting 
westward of the off-shore conditions of the sea, there went on a corre- 
sponding shifting of several faunas that were adjusted to each phase of 
those conditions. 
These facts were stated in a paper on the classification of the upper 
Devonian published in 1885.? 
§ 2. The Appearance of Dominant Species of a General Fauna in 
Reversed Order of Succession at the Close of a Fossiliferous Zone.— 
The case of Spirifer levis in the Ithaca Zone and of the frequent ap- 
pearance of Leiorhynchus at the opening and close of a fossiliferous 
zone were among the earliest observed facts suggesting the actual shift- 
ing of the body of the fauna entering the area in one order of succession 
and its departure in the reverse order. In the Ithaca section there 
occurs at the base of the fossiliferous zone of the Ithaca member a bed 
containing abundance of Spirifer (Reticularia) levis. The discovery 
of the same species at the top of the fossiliferous zone as the normal 
Ithaca fauna become sparse gave the first suggestion that the faunas 
were moving or shifting. The Reticularia zone marked the first trace 
of the fauna to enter and the last to leave the area. Confirmatory evi- 
dence was also found in the order of succession of the dominant species 
of the Ithaca fauna. ‘These facts were reported in 1883.3 
§ 3. The study of the mode of occurrence of Leiorhynchus still fur- 
ther drew attention to the definite order in which series of species came 
in and went out of any given area. The species of the genus were 
generally found abundantly at the base or at the top of the fossiliferous 
zones rich in the brachiopods in the midst of which Letorhynchus was 
rare.* 
§ 4. The reappearance in a single or few strata of several represen- 
tatives of an earlier fauna long after the formation to which they were 
normal had ceased. 
Slight traces of this fact were observed in the first survey of the 
Devonian section passing through Ithaca, reported in 1883, Bull. 3, 
U. 8. G. S., and the fauna No. 14 N (p. 15) was called a recurrent 
Hamilton fauna because of the appearance there of such species as 
Spirifer fimbriatus, S. augustus, Pleurotomaria capillaria and others; 
*Proc. American Association for the Advancement of Science, XXXIV., 
. 222. 
; * Bull. 3, U. S. G. S., p. 20, and 1885 Proc. A. A. A. &., Vol. XXXIV., p- 
222, ete. 
“see Bull, 3, U. S, G. 8: pp. 16 and 17, 1883. 
