36 



Report or the State Geologist. 



deposits of adjacent provinces. The Oneonta formation thus represents the 

 later portion of Portage time in the sections along the Chenango river and to 

 the east. The formation is continued into the Helderberg mountain and the 

 more southerly foot hills of the Catskills.* 



Above the Oneonta sandstones the fauna of the central region is but 

 sparingly represented, and when so, in association or oscillation with a true 

 Chemung fauna, in the normal manner of replacement of a given fauna by its 

 successor in the same province. 



In regarding the various faunas above considered as distinct organic 

 associations coexistent during Portage time in this geographic amphitheater of 

 New York, interpolated outliers or stragglers from each are to be expected in 

 the provinces of ihe others. Thus in the western or Naples province there 

 are occasional appearances of species usually brachiopodous, which appertain 

 to the adjoining eastward or Cortland province. Now and again are to be 

 found thin sandstones which contain such forms as Leptostrophia mucronata, 

 OrtJtothetes cf. arctostriata, Productella, Strophalosia, Liorhynchus ; forms 

 which do not strictly belong to the Naples fauna ; nor are they associated 

 with its species, being found in this region by themselves and rarely in the 

 softer shales in which the Naples species especially predominate. Such strag- 

 gling associations of the eastward species are small, and yet have sometimes 

 gone surprisingly far afield, having evidently, from their fragmentary and 

 massed condition, been carried in by the movements of the water. In similar 

 manner we have observed some members of the Otselic fauna reappearing 

 briefly above the Oneonta sandstones ; Spirifer laevis and Leptostrophia 

 mucronata^ in the proemial Chemung fauna exhibited in the sections near 

 Greene, Chenango county (See 15th Ann. Rept. N. Y. State Geol.1898). 



From the foregoing brief consideration of these regionally approximate 

 but distinct faunas which are included within the limits of Portage time, it 

 will be clearly seen that while the term Portage group, signifying in its 

 accepted sense the series of strata between the Tully limestone or Genesee 

 slate-f- and the Chemung formation, has a definite value, there is no exactitude 



* In the regiou east of the Chenango river the absence from the series, of the Tully limestone and Genesee slate, leaves 

 a uniformity of Iithologic composition to the strata both below and above this horizon. We owe to the careful investiga- 

 tions of Prof. C. S. Prosseb the determination in these arenaceous shales of the horizon of the Tully limestone, as marked 

 by the presence of Hypothyris venustula (-Rhynchonella cuboides); Fifteenth Ann. Rept. N. Y. State Geologist. 



t The Genesee slate has generally been classified in text books and referred to in the volumes of the Palaeontology of New 

 York and elsewhere, as the uppermost subdivision of the Hamilton group. While the disposition of such a fauna is often a 

 matter of convention and while horizontal planes of division must be drawn, it is a truer expression of the faunal affinity of 

 the fDrmation to include it within the Portage group, as long ago suggested by the writer. This disposal 

 of these beds was foreseen by Prof. James Hall, who, in a foot-note to page 218 of his report on the Geology of the 

 Fourth District ( 1843), made the following remark apropos of the name proposed for the formation; "From 

 the circumstance that other shales above this appear in the same gorge [Genesee river at Mt. Morris], it would have been 

 desirable to give another name ; but no locality is known which is not more objectionable than this. Since it is very 

 probable also, that this rock will in future be considered only as a member of the Portage group, its local name will be the 

 more appropriate." 



