Page:Popular Science Monthly Volume 77.djvu/78

72 and higher up in the midst of the Chemung section at Chemung narrows 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 U. 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 fossiliferous zones; the separate zones of the two series alternate 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 formation.

The second set of zones includes the Hamilton fauna proper and recurrent representatives of that fauna which I have named the Paracyclas 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 Swartwood Tropidoleptus zones, respectively). All of these several fossiliferous 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 thickness 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