288 H. S. AVILLIAMS SHIFTING OF DEVONIAN FAUNAS 



series of fossiliferous zones, the separate zones of the two series alternat- 

 ing in succession. 



The zones of one series dominate the western sections of the area, and 

 thus thin out or disappear on tracing them eastward. The zones of the 

 second series dominate the eastern sections, and particularly the whole 

 eastern New York sections, but thin out westward, and in some cases are 

 entirely wanting in sections west of the Watkins Glen quadrangle. 



The first set of faunal zones includes the faunas of the Genesee shale, 

 the Portage formation, and the several divisions of the Chemung forma- 

 tion. 



The second set of zones includes the Hamilton fauna, proper and recur- 

 rent representatives of that fauna, which I have named the Paracyclas 

 lirata zone; the Spirifer mesistrialis zone; the Leiorhynchus glohuli- 

 formis, or Kattel Hill zone (representing the typical Ithaca group of 

 Hall at its typical sections at Ithaca) ; and the first, second, and third 

 recurrent Tropidoleptus faunas, which I have called the Van Etten, the 

 Owego, and the Swartwood Tropidoleptus zones. 



All of these sev.eral fossiliferous zones of the second set become de- 

 cidedly thin on passing westward across the region. 



The Ithaca fauna is occasionally detected west of the Watkins Glen 

 quadrangle, but is confined to less than 100 feet at Watkins, is recognized 

 for 300 feet at Ithaca, and ranges through at least 600 feet along Tiough- 

 nioga Eiver. 



Only a slight trace of the Paracyclas zone is seen as far west as Ithaca, 

 but is well expressed in the sections on the east side of the area. 



The Van Etten, Owego, and Swartwood Tropidoleptus zones appear in 

 thin tongues of strata as far west as the Waverly quadrangle and are 

 seen in occasional traces as far wTst as the Elmira quadrangle, and when 

 followed eastward appear to blend together as a modified Hamilton fauna, 

 sparsely appearing in the strata up to the arrival of the Catskill type of 

 sedimentation. 



LIMITED RANGE OF RECURRENT SPECIES 



Where the Hamilton recurrent zones are seen in sharpest exprssion the 

 recurrent species range through only a foot or a few feet of strata, hold 

 in abundance four or five characteristic Hamilton species, such as Tropi- 

 doleptus carinatus, Cypricardella hellistriata, Rhipidomella vanuxemi, 

 Spirifer marcyi and Delthyris mesicostalis, cf. D. Consohrinus, and others, 

 and the Owego and Swartwood zones appear in the midst of a character- 

 istic Chemung fauna present both above and below each recurrent zone. 



