72 THE POPULAR SCIENCE MONTHLY 



and higher up in the midst of the Chemung section at Chemung nar- 

 rows Tropidoleptus carinatus and Cypricardella bellistriata, Phacops 

 bufo and Dalmanites calliteles were found. 



The discovery of such traces of an earlier fauna led to further 

 search; and as the evidence accumulated an elaboration and definite 

 formulation of the theory of recurrence of faunas was made which has 

 been set forth in several papers, and is illustrated in detail in the folio 

 of the Watkins Glen-Catatonk quadrangles, which is now in press, for 

 the TJ. S. Geological Survey (December, 1909). 



The facts there brought out are substantially as follows : There are 

 exhibited in the sections mapped for the quadrangles two series of fos- 

 siliferous zones; the separate zones of the two series alternate in suc- 

 cession; 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 quad- 

 rangle. The first set of faunal zones includes the faunas of the Gene- 

 see shale, the Portage formation and the several divisions of the 

 Chemung formation. 



The second set of zones includes the Hamilton fauna proper and 

 recurrent representatives of that fauna which I have named the Para- 

 cyclas lirata zone, the Spirifer mesistrialis zone, the Leiorhynchus 

 globuliformis or Kattel Hill zone. These zones are represented by the 

 typical Ithaca group of Hall in its typical sections at Ithaca ; and above 

 them appear the first, second and third recurrent Tropidoleptus faunas 

 (which I originally named the Van Etten, the Owego and the Swart- 

 wood Tropidoleptus zones, respectively). All of these several fossilifer- 

 ous zones of the second set become decidedly 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 thick- 

 ness at Watkins, is recognized for three hundred feet at Ithaca and 

 ranges through at least 600 feet along Tioughnioga River. 



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

 Ithaca, but it is well expressed in the section 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 west as the Elmira quadrangle. 

 When followed eastward they appear to blend together as a modified 

 Hamilton fauna sparsely appearing in the strata up to the income of 

 the Catskill type of sedimentation. 



Where the Hamilton recurrent zones are seen in sharpest expression 

 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 



