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 heing 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 



§ 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 Sp infer leevis in the Ithaca Zone and of the frequent ap- 

 pearance of Leiorliynchus 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) losvis. 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 Leiorliynchus 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 Leiorliynchus was 

 rare. 4 



§ 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. S. 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. august us, Pleurotomaria capillaria and others; 



2 Proc. American Association for the Advancement of Science, XXXIV., 

 p. 222. 



3 Bull. 3, U. S. G. S., p. 20, and 1885 Proc. A. A. A. 8., Vol. XXXIV., p. 

 222, etc. 



4 See Bull. 3, U. S. G. S., pp. 16 and 17, 1883. 



