72 THE POPULAR SCIENCE MONTHLY 
and higher up in the midst of the Chemung section at Chemung nar- 
tows L'ropidoleptus 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 U. 8S. 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 Letorhynchus 
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 T 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 
