TRANSACTIONS.

THE UTICA SLATE AND RELATED FORMATIONS OF THE SAME GEOLOGICAL HORIZON.

BY C. D. WALCOTT.

[Read before the Albany Institute, March 18, 1879.]

THE UTICA SLATE.

Mohawk slate, Black slate and shale, Frankfort slate, Graptolitic slate, Lorraine shales (in part) of the New York Geological Reports.

In part Professor Eaton's Transition argillite, Wacke slate and Glazed slate. No. 3 and the Matinal Black slate of the Pennsylvania Survey.

The name Utica slate was adopted by the New York geologists in their final reports for the black bituminous slates succeeding the Trenton limestone in the Mohawk and Black River valleys - Prof. E. Emmons retaining the term Lorraine shales for the upper portion beneath the shaly sandstones of the Hudson River group, or Lorraine sandstones as he termed them. The term Hudson River group, with the Utica slate for a subdivision embracing the lower slaty portion, was, however, generally received into geological no

menclature.

At the typical locality in the vicinity of Utica the formation has a thickness of over 600 feet, the upper part passing into the lighter colored, more silicious slate, beneath the Oneida conglomerate; this change of color and addition of silicious material, with the presence of a few thin sandy layers, alone representing the arenaceous shales and sandstones of the Hudson River group in its extension east and west from this point. The Utica slate would otherwise be

a continuous formation from the Trenton limestone to the base of the conglomerate.

At Rome, fifteen miles west, the shaly sandstones increase in Trans. x.]

1

thickness, and contain characteristic fossils of the Hudson River formation above the Utica slate, namely: Ambonychia radiata, Modiolopsis modiolaris, Cyrtolites ornatus, etc. The extensive development of this portion of the group in the valleys of the Black, Salmon and Hudson rivers, and its almost entire absence near Utica, is undoubtedly owing to some local cause which affected the distribution of the coarser sediments.

The Utica slate formation was traced by the New York geologists down the Mohawk valley from Oneida county through Herkimer, Montgomery, Schenectady and Saratoga counties to the shores of the Hudson. At Baker's Falls, Saratoga county, it is seen in contact with, and resting upon, the Trenton limestone. It here contains graptolites characteristic of the formation in Central New York and also the typical fossil of this horizon, Triarthrus Becki. Trilobitic remains are very rare in localities where graptolites abound in the undisturbed slates in Oneida county. This is particularly noticeable in the graptolitic slates of the Hudson River valley, where the graptolitic fauna flourished to the almost entire exclusion of other forms common to the slates elsewhere.

Prof. Wm. W. Mather gives the following localities in the Hudson river valley below Baker's Falls, where the Utica slate is to be observed with its characteristic graptolites: at Waterford, Cohoes, Norman's kill below Albany, at Hudson, and also one and one-half miles below on the same side of the river; in the black slate of the Shawangunk mountain, one and one-half miles east of Ellenville, Orange county; also at Blue Rock in Marlborough on the bank of the Hudson several miles below Poughkeepsie. Owing to the disturbed condition of the strata the graptolites afford the means of determining the geological horizon, where, without their being present, it would be exceedingly difficult if not impossible to do so.

Prof. R. P. Whitfield, in a letter written to Dr. C. A. White, gives a very full description of the occurrence of the graptolites at Norman's kill and the evidence they afforded of the equivalency of the graptolitic slates and the Utica slate.

Prof. Mather included a greater range of rocks in the Hudson River group, on the east side of the Hudson, than is now recognized as belonging to it. The evidence, however, that he adduced in 1843

1 Geol. of N. Y. Surv. First Geolog. Dist., pp. 393-395. 1843.

2 It is interesting to note in this connection that Mr. T. Nelson Dale, Jr., has recently discovered typical Hudson River group fossils in this same vicinity. Amer. Journ. Sci. Arts, XVII, p. 57. 1879.

Wheeler Expd. West of the 100th Meridian, IV, Pt. I, Pal.,

p. 19.

1875.

of its presence, with its lower division the Utica slate, in the valley of the Hudson, was very complete, and, judging from the writings of his associates on the geological survey and contemporary writers, accepted as conclusive. Of the controversy which arose at the time of the making up of the Quebec group, regarding the age of these rocks along the Hudson and the retaining of the term Hudson River group in geological nomenclature, a very complete review will be found in a paper recently published by Prof. James Hall.'

Passing to the south-west along the line of the Appalachians, we find the Utica slate mentioned by Prof. H. D. Rogers, as occurring in the long valleys crossing the southern, central half of the state of Pennsylvania and into Virginia. In the Kittatinny and Kishicoquillas valleys it has a thickness of from 300 to 400 feet and carries graptolites, also Triarthrus Becki.

South-westward in Virginia the black slate passes into the drab colored shales of the Nashville group of Tennessee, reference to which will be made in reviewing the formations of the Utica slate horizon. The northern extension of the formation from Baker's Falls, Saratoga county, is seen in the numerous outcrops in the Champlain valley and down to the St. Lawrence river, where it expands and extends from Montreal to below Quebec. An outlier at Lake St. John, and the presence of the slate in the channel between the Mingan Islands and the Islands of Anticosti, gives the known extension to the north and north-east. Of its presence at Anticosti Sir William

Logan says:3

"Loose fragments of black, strongly bituminous graptolitic shales, in every way resembling those of the Utica formation, and of some of the interstratified beds of the Hudson River, are met with on the beach on the north side of Anticosti."

Graptolites abound at Lake St. John and Triarthrus Becki also occurs. West of Montreal numerous outliers of the Utica slate are found in the Ottawa basin. Asaphus Canadensis, which occurs so abundantly at Collingwood on Georgian Bay, is found near the city of Ottawa associated with Triarthrus Becki and other characteristic fossils of the Utica slate formation.

1 Proceed. Amer. Assoc. Adv. Sci. 1877.

? Professor C. H. Hitchcock, in the Science News of March 15, 1879, states that Professor B. K. Emerson of Amherst College, has in his possession specimens of Triarthrus Becki Climacograptus bicornis, etc., from the Arctic regionsbr ought by Captain Hall; thus proving the presence of the Utica slate horizon to the north of any previous known exposure.

Geology of Canada, p. 221., 1863.

Having traced the extension of the formation down the Mohawk valley to the Hudson and thence north, north-east, and south-west, we return to Utica and follow it to the north-west across Oneida, Lewis and Jefferson counties to the eastern shore of Lake Ontario. It outcrops on the shore east of Toronto, on the north side of the excavation made in the strata by the lake basin, and, crossing the province of Ontario in a north-westerly direction, presents a fine exposure at Collingwood on Georgian Bay. With a more westerly trend it is next seen crossing the northern side of Manatoulin Island in Lake Huron, beyond which, in its characteristic black bituminous shaly formation, it has not been traced.

On Manatoulin Island the thickness has decreased to fifty feet (Logan).

Dr. C. A. White' mentions the discovery in black slates in Nevada of Graptolithus quadrimucronatus, G. pristis, and two species allied to forms found in the Utica slate. This discovery will have an important bearing on the extension of the Utica epoch to the western side of the continent, should it be substantiated by subsequent investigation.

The Trenton limestone and the strata of the Hudson River formation are co-extensive with the geographical range given for the Utica slate. In many instances it is difficult to indicate the line of demarcation between the latter formation and the strata above or below, while in other localities the limits of each formation are clearly defined. In Jefferson county, N. Y., it is only by an arbitrary line that the Utica slate can be separated from the Hudson River formation. In the town of Deerfield, Oneida county, N. Y., the Trenton and Utica formations are as intimately connected, lithologically, as the Utica formation is with the succeeding Hudson River formation, which is also the case to the north-east on the St. Lawrence and in other localities.

Prof. H. D. Rogers in the Pennsylvania Survey Report, 1858, says: "The transition from the formation of this very fossiliferous limestone (Trenton) to that of the bluish black, carbonaceous, matinal (Utica) shale, was, throughout most of the basin, now accessible to study, somewhat abrupt; though, as we have seen, it was extremely gradual in one part of their south-east outcrop, or in the northern section of the great valley of Virginia. There, there is such an intermingling of the materials, and even of the fossils of the two strata, that a division of the blended mass is difficult if not impossible.

1 Wheeler's Expd. West of the 100th Meridian, IV, Pt. I, Pal., p. 10, 1875. * Emmons's Agriculture of New York, 1, p. 123. 1846.

3 Geology of Canada, p, 202. 1863.