Ithaca formation, which has been demonstrated to lie below the Chemung in the Ithaca section," is opposed to the supposition that the horizon now under investigation is as high as the typical Chemung formation of western New York.

Finally, there are 25 species which have not been recorded in the region below the base of what is there called the Chemung formation. These are tabulated in Table XXVIII.

TABLE XXVIII.-Species which occur above the Oneonta formation but not in the Ithaca formation of the eastern counties.

The species starred are mentioned in more than one faunule; those not starred were positively identified but a single time in all the faunules analyzed. On the right of the starred species are numbers indicating, first, the number of positive identifications, then the number of doubtful specific identifications. When the number of doubtful identifications is large, variation is probably great.

Only 3 of these 25 species belong to the standard list of dominant species of the western Chemung (see Table XXI). These are: Spirifer disjunctus.

Productella lachrymosa.
Camarotœchia contracta.

As has already been said, the first and last of these are reported but once. On the other hand, the fauna contains Pugnax pugnus, which is characteristic of the typical Ithaca fauna, but does not belong to the typical Chemung fauna of western New York.

On the other hand, the following table (Table XXIX) shows a prominence of species which in the western New York Devonian are characteristic of an earlier stage in faunal development than that of the Spirifer disjunctus fauna.

TABLE XXIX.-Dominant species above the Oneonta not confined to the horizon of the Chemung formation in western New York.

Spirifer pennatus posterus.

S. mesistrialis.

Camarotœchia stephani.
Cypricardella gregaria.
Tropidoleptus carinatus.

Delthyris mesicostalis.

Pugnax pugnus.

Chonetes setigerus.
Camarotœchia eximia.

Palæoneilo constricta.

a Bull. U. S. Geol. Survey No. 3, 1884, p. 28.

CHAPTER IV.

SHIFTING OF FAUNAS,

EVIDENCE OF SHIFTING OF FAUNAS ASSOCIATED WITH

DEPOSITION OF ONEONTA SANDSTONE,

In considering the evidence contained in the tables of statistics already presented, it is important to note the following points: The strata lying above the Oneonta sandstone and below the Catskill, in the eastern counties of New York, contain a fauna in which there are 27 species of the Tropidoleptus carinatus fauna, 5 of which are among its most characteristic 12, and 25 of which are reported from genuine Ithaca formation strata. The fauna contains 8 species which are found in the underlying Ithaca formation, but have not been recorded for the Hamilton of this region; 3 of these are in the list of dominant species of the Productella speciosa fauna. Finally, there are 25 species not recorded from the formations below in the same region, 4 of which are among the dominant species of the Spirifer disjunctus fauna, but only one of these forms is at all dominant in the eastern fauna under investigation."

The evidence points clearly to a position intermediate between the typical faunas of the Hamilton and Chemung formations. That the rocks are younger than the Hamilton formation is shown both by stratigraphical evidence and by the occurrence of species that have never been discovered in the Hamilton formation. That they are not of the same horizon as the Chemung formation containing the pure Spirifer disjunctus fauna is shown by the absence of most of the dominant species of that fauna, as well as by the strong representatives of typical species of the Tropidoleptus carinatus fauna; and that they are later than the typical Ithaca formation is shown by the presence of a few forms not occurring so low as the Ithaca formation of the central and western parts of the State.

The paleontological statistics are thus conclusive in demonstrating the intermediate place of the post-Oneonta fauna between the typical Productella speciosa fauna of the Ithaca formation, and the Spirifer, disjunctus fauna of the Chemung; but it does not follow that the rocks are intermediate, and therefore not represented in either the Portage or Chemung formations farther west. The exact stratigraphical equivalency may be shown by a close study of the particular local characteristics of the faunules themselves.

This temporary phase of the general fauna of the zone following

Bull. 210-03-7

a See Tables XXV to XXIX,

97

the Oneonta sandstone was recognized and named in 1886" as the "Leiorhynchus globuliformis stage of the Middle Devonian fauna." The gibbous form of Leiorhynchus, under the name Atrypa globuliformis, was noted by Vanuxem as existing in myriads in the "Chemung group" of the third district, "numerous localities abounding with it."b

The close relationship between the species so abundant in the arenaceous strata overlying the Oneonta sandstones of Chenango and Otsego counties and the common flattened form Leiorhynchus mesicostale was recognized by Hall.

d

The presence of the species in the Ithaca formation was noted in 1884, also the fact that in the rocks about Ithaca the form called Leiorhynchus mesicostale was found in the softer argillaceous shales, "while in the more arenaceous beds the convex forms L. globuliforme and L. kellogi appear." The great variability of the specimens in any handful led to the belief there expressed

that the representatives of the genus Leiorhynchus, found in the Devonian of New York at least, offer no better claim to specific distinction than do the various forms of Atrypa reticularis, although the variations of form and the relative prevalence of certain variations are valuable and, we believe, sensitive indications of changed conditions of environment.

The association of gibbosity of form with sandy sediments gave occasion for expecting the species to appear in the sediments following the Oneonta sandstone in the Chenango Valley, and that this species should appear there in place of Leiorhynchus mesicostale was looked upon not as indicative of a new species, but as evidence of changed conditions of environment modifying varietally the common Ithaca form.

Another fact has been observed in the course of these studiesLeiorhynchus occurs very often in the rocks among the first species of brachiopods to appear in running up a section after a barren place in the strata. This was interpreted as an indication that the genus was adapted to live in conditions unfavorable to the life of most of the brachiopods. It was noticed in the Chenango Valley region that Leiorhynchus globuliforme was among the earlier species to appear above the sands and flags (nearly barren of marine invertebrates) above the horizon of the Oneonta sandstone. The fact that the species appeared in the Ithaca formation associated with the characteristic species of that formation, and was particularly associated with the hard sandstone beds, which were distinctly purple in color, led to the suspicion that this Leiorhynchus globuliforme fauna was a representative of the Productella speciosa fauna of the Ithaca formation, but a little later in age.

This theory of a shifting of the fauna across central New York from

a Proc. Am. Assoc. Adv. Sci., Vol. XXXIV, p. 226.

b Geology of Third District of New York, p. 182,

e Paleontology New York, Vol. IV, p. 364.

d Bull. U. S. Geol. Survey No. 3, p. 16.

the east toward the west during the time of the sedimentation of the Portage and Ithaca formations of the Cayuga Lake meridian was suggested by the fact that in the neighborhood of Ithaca, on passing upward from the Genesee shale, there is an increase of species of the Tropidoleptus fauna with the withdrawal of the Portage species. The shifting was reversed after the center of the Ithaca formation was passed, as was shown by the reappearance of the species of the Portage formation (in reverse order) on ascending the strata, until above the Ithaca formation, with its dominant marine invertebrate fauna, came several hundred feet of sediments quite similar to the typical Portage of western New York and holding the Cardiola speciosa fauna.

This shifting of the fauna first westward and then eastward was such as to make the true succession of the faunas take a wedge-shaped position in the sediments rather than make a continuous superposition of formations in one column. The Oneonta formation pushed westward into the midst of the Ithaca formation of Ithaca, and as it ceased as a formation, by the withdrawal eastward again of the peculiar kind of sedimentation, the Ithaca formation also pushed eastward, but the fauna in the latter expressed a later stage of evolution in Chenango County than in Tompkins County.

Taking this view of the case the Oneonta formation is, stratigraphically, at the same horizon as the middle of the Ithaca formation of the Ithaca section, which is also at the same horizon as the midst of the Portage formation of the Genesee Valley section. The fossiliferous zone above the Oneonta, in Chenango and Otsego counties, is the stratigraphical equivalent of the barren 300 or 400 feet of the Ithaca section and the fossiliferous beds of Caroline, which lie between the fossiliferous Ithaca formation with the Productella speciosa fauna and the Chemung formation with the Spirifer disjunctus fauna.

The geographical shifting of faunas coincidently with the accumulation of sediments not only is consistent with all the facts which have so far come to light, but there is no other theory advanced by which the bewildering confusion in the relations of the faunas of this region is satisfactorily accounted for.

The place of the Oneonta sedimentation is recognized in the sandstones and flags in the midst of the Ithaca formation, and the Oneonta, by its becoming thicker and more strongly marked on passing eastward in Chenango and Otsego counties, is seen to have its origin from that direction.

The black shales of the Genesee and the following fine mud shales of the Portage of western New York containing the Cardiola fauna (Glyptocardia speciosa) thin out eastward; but the proposition that they occupy the place of the Portage and Ithaca formations of the central part of the State, in which is a fauna rich in species of the Tropidoleptus fauna, is proved by the statistics collected by Messrs. Prosser and Clarke.

The difficulty found in discussing this problem has been due in large measure to the lack in common usage of any way to deal with the fauna independently of the name and classification of the geological formation to which it is said to belong.

In the present case, in order to treat of the subject in hand with the nomenclature already in use, it is necessary to say that the rocks and their fossils appearing in the section of Chenango and adjacent counties, above the Oneonta sandstone, are either Ithaca, Oneonta, or Chemung. There seems to be no other way of designating them; the use of the word transition is only an avoidance of decision. But if one speak of the formation as Chemung, the necessity arises of assuming the fauna to be equivalent to some part of the fauna of the Chemung formation where typically exhibited. This, as has been shown, is not correct, if by the "typical exhibition " be meant a case in which the separation between the Ithaca and Chemung faunas is sharply defined. If a case be taken in which the mingling of the two faunas is evident, it is not properly a typical exhibition. But in the list of species from these rocks in Greene Township, Chenango County, there is an undisputed mingling of a large number of species of the standard Tropidoleptus fauna with a considerable number of species of the standard Spirifer disjunctus fauna, and a still larger number of species whose most central stratigraphical position is in the standard Ithaca formation.

If now we are to deal with the formations as such, the evidence seems to be very strong for the opinion that the part of the actual column of the Genesee section of western New York, called the Portage formation in the reports, when followed stratigraphically eastward is represented not only by the Oneonta formation of Otsego and adjacent counties in the eastern part of the State, but by the fossiliferous beds lower down, and by some, at least, of the fossiliferous beds following the Oneonta.

Even if we were to suppose, with Dr. Clarke, that the Oneonta sandstone is the formational equivalent of the "Portage sandstone,"a this does not dispose of the essential problem; because the equivalency does not include likeness of species in the two formations.

The fauna in the beds below the Oneonta sandstone is more diverse from the fauna immediately preceding the Portage sandstone of western New York than it is from the fauna preceding the Genesee shale of the same column. The fauna following it is also less like the fauna following the Portage sandstone than it is like the fauna of the Ithaca formation, which is known to be stratigraphically below it. If the formational equivalency were in fact as Clarke supposed it to be, the term equivalency would not carry with it the meaning that the beds. were deposited at the same epoch of geological time.

The actual tracing of the beds step by step across from Otsego to Allegany County would settle the question as to time equivalency,

aThirteenth Ann. Rept. State Geologist New York, 1893. p. 557.

3 See

p.

117.