Study of the Middle Cambrian faunas has made possible a very precise correlation of the strata with those of northern Europe and the western United States. Thanks also to several people who provided valuable help during the course of the fieldwork. Fisher contributed his knowledge of the area and suggested the investigation of several potentially fossiliferous exposures, some of which were productive.
Almost all the material, except for a few Lower Cambrian trilobites of the Elliptocephala asaphoides composed of shale deposits at. In the wooded area just north of the Griswold farm are several isolated outcrops, some of which have produced a few, very fragmentary fossils.
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NO, 4 TRILOBITES, TACONIC SEQUENCE — RASETTI Q
Lower Cambrian Pagetides fauna was collected from about a dozen outcrops of underlying limestone in the NW quarter of the EastChatham quadrangle, in addition to the Griswold Farm and Maiden Bridge roadcuts discussed previously. Two outcrops located on the Lopez farm, east of the Nassau-Maiden Bridge road, have yielded interesting Pagetides faunules. Some of the rocks at Ashley Hill are the usual coquina of Elliptocephalaasaphoides fragments, and sometimes yield well-preserved examples of the smaller trilobites, in addition to many.
Hudson North Quadrangle: Judson Point.— A continuously exposed section of about 250 feet of strata in suitable sedimentary sequence occurs along the tracks of the New York Central Railroad on the east shore of Hudson Riverat Judson Point. Fossils also occur in a 2-5 inch bed of partly blackened sandstone 52 feet above the top of the black shale.
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INDEX OF LOCALITIES
BIOSTRATIGRAPHY LOWER CAMBRIAN
Lochman (1956) inventoried the fossils of the Elliptocephala fauna and compared the composition of that assemblage with faunas from other areas of North America and Europe. The collection from separate block CS-15/L3 can probably be included in the collection, as most species are common. Although the Acimctopushilohatus fauna apparently has no trilobite species in common with the Elliptocephala asaphoides fauna, the representation of the different trilobite families is similar in terms of the abundance of individuals of Eodiscidae and Olenellidae, in the absence of Agnos.
In both the Griswold farm and Maiden Bridge roadcut sections, the earliest faunal of the Pagetides fauna, the Neopagentina taconica fauna, stratigraphically overlies the beds that bear the Acimetopus fauna. In the previous paper (Rasetti, 1966a, p.21) it was pointed out that the discovery of Bolboparia canadensis, closely related to one of the Eodiscidae in the Acimetopus bilobatns fauna, in the Lower Cambrian.
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In this respect the Pagetides fauna of the Taconian series has less in common with the typical late-early Cambrian faunas of the Appalachian and Cordilleran provinces, and shows some affinity with the faunas of the Acado-Baltic province of North America and Europe, where the Eodiscidae are well represented. In the Pagetides fauna, however, the Acado-Baltic character is less pronounced than in the fUliptocephala asaphoides and Acimetopus bilobatus faunas, where the Eodiscidae predominate. Species of Pagetides are also known from the Olenellus Shale of Appalachia Province, as Pagetides elegans occurs (Rasetti, 1948a) in the Parker Shale at the Kelly Quarry near Swanton Junction, Vermont, and the commonly, but not specifically, identifiable Pagetides. parkeri (Walcott) was described from the same formation at the classic locality near Georgia, Vermont (Rasetti, 1952, p. 439).
Undescribed, poorly preserved specimens of Pagetides from the Kinzers Shale of the Lancaster, Pennsylvania Basin are preserved in the United States. In New York State, the Pagegetides fauna has never been observed in conglomerate rocks, in contrast to the more common mode of occurrence of the Elliptocephaln fauna.
MIDDLE CAMBRIAN
Fauna of the Bathyiiriscus-EIrathina Cone.— The oldest Middle Cambrian fossils known from Columbia County, and the Taconic sequence in general, belong to the Bathyuriscus-Elrathina Zone. A comparison of the Bathyuriscus eboracensis fauna with the series of genera and species in the. Sweden is known only from the two upper zones, C2 and C3, of the Paradoxides forchhammeri stage.
Three of the species, BatJiyuriscus eboracensis, CorynexocJiidesf expansus, and Hypagnostus parvifrons, are common to the Stockport Station fauna. In Sweden, Centropleura (Westergard, 1953) occurs in the Solenopleura bracJiymetopa Zone (C2) of the Paradoxides forcJi- Jiammcristage.
SYSTEMATIC DESCRIPTIONS
However, in the absence of pygidium, the same uncertainty as discussed for the previous species prevails. Description.-Glabella of the same proportions as in the preceding species, with the frontal lobe slightly wider than the posterior lobe. Discussion.- Among theagnostid cephala recovered at the site, the present one is distinctive, especially along the trans-glabellar furrow.
Discussion.-This species is more typical of the genus than the first. yielding, most differences occur in the cephalon. All furrows have completely disappeared, but for a slightly differentiated, subtriangular part of the posterior border. There is a broad, very shallow depression in front of the raised posterior part of the glabella.
. The occipital ring was apparently differentiated from the glabella, but this part of the cephalon is incompletely preserved. Posterior border short (tr.) due to narrowing of posterior part of cephalon, straight. The only si)ccimcn. The furrows and border margin are both narrow but well defined, neither is preserved in the posterior half of the cephalon.
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There is indication of the occipital groove as a pair of lateral impressions, Geneae with moderate relief. A relatively large glabella, 5 mm. in length including the occipital ring, shows faint ornamentation in the fingerprint pattern. The species is mainly characterized by the arrowiness of the frontal glabellar lobe and the well-defined, narrow rim around the palpebral lobes.
3 in the narrow border, but the position of the intergenal spine is Hke in species no. Discussion.- The glabellar lobation and width of the inner part of the cheeks is similar to species nos. Rather, there appears to be a small spine at the posterior margin of the occipital ring.
Hypostome refers to the species of the general corynexochoid form, characterized mainly by the large forward expansion of the anterior lobe. Posterior area not completely preserved in any of the larger cranidia, slender as usual in the genus. Discussion.—This species appears closest to Bathyuriscus fimbriahisRobison (1964a) from the lower part of the Bolaspidellazone of Utah.
At both locations in association with Ptychagnostus gibbus and other trilobites of the Bathyuriscus-Elrathina zone. Discussion.—This form is typical of a group of 6-spine species most common in the Middle Cambrian. The cranidium is also distinctive in the vertical slope of the gcnae anterior to the eye ridges.
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Occurrence.- Loose block cs-7/M3, associated with Pagetia erratica and other trilobites of the Bathyuriscus-Elrathina zone. Palpebral area, palpebral lobe, ocular ridges and border as in typical forms of the genus. Discussion.—This pygidium has many of the features of Hemirodon, differing chiefly in the posterior curve of the anterior border furrow.
The appearance of the broken test suggests that there may have been a lateral spine, an extension of the flat part of the rim. The rest of the pygidial margins are broken off and it cannot be ruled out that there may have been several pairs of spines. The thoracic segment, belonging to the anterior or middle part of the thorax, shows the characteristic short (tr.) pectorals and a diagonal pleural furrow.
Prevent. - Collection cs-23 {Centropleura faunule), Judson Point. DiscUrSsion. - The fragmentary material presented herein, while adding nothing to the knowledge of the genus, is of considerable biostratigraphic significance, indicating the presence of late Middle Cambrian strata in the Taconian sequence. and the relationship of the fauna to the Acado-Baltic province. The facial suture must have been completely marginal as it does not cut off any part of the edge. Occurrence.– Most of the illustrated specimens come from loose blocks on the Griswold farm (coll. cs-7/Ml and cs-8/Ml).
The immature cranidia are remarkably similar to specimens of the same size calculated by Hutchinson (1962). Anterior facial sutures not distinct, curved inwards and rounding the anterior angles of the cranidium. The border extends inwards to form part of the posterior border of the cephalon, and the facial suture shows an acute angle corresponding to the termination of the posterior region of the cranidium.
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The species has been found at several locations in the Taconic Series, almost always in shales, even though other members of the Elliptocephala asaphoides assemblage are much more common in limestones. The skull of Rimouskia typica is virtually identical to that of Atops trilineatus, except for the facial suture and the presence of optic lobes. Frontal area moderately transversely curved; preglabellar field short (saggy), approximately equal to the width of the medial border.
The anterior position of the palpebral lobe is the only characteristic that does not conform to the typical forms of the genus. Anterior facial sutures definitely convergent in front of eyes, perhaps marginal for a short median part;. Discussion.—This generalized ptychoparioid resembles several genera known from the Lower Cambrian of North America, but the parallel-sided glabella, the anterior position of the eyes, and the narrowness of the frontal portion of the cranidium are somewhat unusual.
It is possible that these features are emphasized by the immaturity of the specimens. Fixigenae convex and descending, wider posteriorly, the facial sutures continuing the outline of the anterior border without major change in direction. In the discussion of the faunas, it was shown that associated fossils give a strong indication for Late Middle Cambrian.
Relatives of the above genera are known from late Middle Cambrian strata, such as Catillicephala in the St. Discussion. This pygidium, although the proportions are the same as in most ptychoparioid genera, has characteristic features in the small number of axial segments, flatness of the pleural areas and lack of differentiated border furrow and margin. The pleural areas are convex and downward sloping, showing four rather deep pairs of pleural grooves, and in the smallest of the specimens depicted distally imprinted interpleural grooves are also seen.
Discussion.- The depth of both pleural and interpleural furrows, combined with the narrow, elevated rim represent unusual features. Notes on the distribution of the fossils in the Lower Potsdamrocks at Troy, New York, with descriptions of a few new species. Collected Articles in Paleontology and Stratigraphy, Institute for Science and I'".\ploration of the .Arctic (Leningrad), no.
Stratigrai)hy, i)aleonto|ogy, and jialeogeograpiiy of lilliptocipluiUi asaplioidcs strata in Cambridge and Hoosic(|uadr;mgles, New York.
LOWER CAMBRIAN TRIUOBITES
MIDDLE CAMBRIAN TRILOBITES
USXM 156658
