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ONTARIO GEOLOGICAL SURVEY Ontario Open File Report 5516

Ministryof The Trilobite Triarthrus in the Whitby Formation (Upper Ordovician) of Southern Ontario and a Natural Biostratigraphic Framework Resources by Hon. Alan W. Pope Minister Pamela Tuffnell and Rolf Ludvigsen John R. Sloan Deputy Minister 1984

OMNR-OGS 1984

Ministry of Hon. Alan W. Pope Minister Natural John R. Sloan Resources Deputy Minister Ontario ONTARIO GEOLOGICAL SURVEY Open File Report 5516

The Trilobite Triarthrus in the Whitby Formation (Upper Ordovician) of Southern Ontario and a Biostratigraphic Framework

by Pamela Tuffnell and Rolf Ludvigsen

1984

THIS PROJECT WAS PART OF THE HYDROCARBON ENERGY RESOURCES PROGRAM (HERP), AND WAS FUNDED BY THE ONTARIO MINISTRY OF TREASURY AND ECONOMICS UNDER THE BOARD OF INDUSTRIAL LEADERSHIP AND DEVELOPMENT (BILD) PROGRAM. Parts of this publication may be quoted if credit is given. It is recommended that reference to this report be made in the following form: Tuffnell, Pamela and Ludvigsen, Rolf 1984: The Trilobite Triarthrus in the Whitby Formation (Upper Ordovician) of Southern Ontario and a Biostratigraphic Framework, 58 p., 10 figures and 4 plates.

Ontario Geological Survey

OPEN FILE REPORT

Open file reports are made available to the public subject to the following conditions:

This report is unedited. Discrepancies may occur for which the Ontario Geological Survey does not assume liability. Recommendations and statements of opinion expressed are those of the author or authors and are not to be construed as statements of government policy.

Open file copies may be read at the following locations:

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Handwritten notes and sketches may be made from this report. Check with the Library or Region al or Resident Geologist©s office as to whether there is a copy of this report that may be borrowed. The Library or Regional or Resident Geologist©s office wfll also give you information on copying ar rangements. A copy of this report is available for Inter-Library Loan.

This report is on file in the Regional or Resident Geologists© office(s) located at:

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The right to reproduce this report is reserved by the Ontario Ministry of Natural Resources. Permission for other reproductions must be obtained in writing from the Director, Ontario Geological Survey.

V.©G. Milne, Director Ontario Geological Survey

111

FOREWORD

The Hydrocarbon Energy Resources Program of the Ministry of Natural Resources consists of four main components. The Ontario Geological Survey is responsible for the conduct of inventories and assessments of the peat, lignite, and oil shale resources of the Province while the Petroleum Resources Section in Southwestern Region is reviewing conventional oil and gas resources. Assessment of potential oil shales involves an integrated program of drilling and analytical studies focussed on four stratigraphic units, viz. the Ordovician Collingwood Member (Lindsay Formation) and Devonian Marcellus and Kettle Point Formations (all in southern Ontario) and the Devonian Long Rapids Formation (James Bay Lowland). This report presents the results of a biostratigraphic study of trilobites from the Collingwood Member aimed at providing more precise local and regional correlation of this potential oil shale unit.

V.G. Milne, Director Ontario Geological Survey

PREFACE

At the time of writing of this report, stratigraphic studies by staff of the Ontario Geological Survey were underway, leading to a redefinition and renaming of the Whitby Formation and associated units. This led to the following publication: Russell, D.J. and Telford P.G., 1983. Revisions to the stratigraphy of the Upper Ordovician Collingwood Beds of Ontario - a potential oil shale. Canadian Journal of Earth Sciences, Vol. 20, p.1780-1790. Thus the stratigraphic terminology used in this report does not reflect current nomenclature used by the Ontario Geological Survey and is based merely on nomenclature published prior to the beginning of this study in 1982 (e.g. Liberty, 1969).

CONTENTS

Abstract Introduction Systematic paleontology Triarthrus beckii Green Triarthrus eatoni (Hall) Triarthrus canadensis Smith Triarthrus rougensis Parks Triarthrus spinosus Billings Stratigraphic terminology Field work and sampling programme Stratigraphy of the Whitby Formation Biostratigraphy Bibliography Appendix of locations of surface and subsurface sections Explanations of figures Explanations of plates

THE TRILOBITE TRIARTHRUS IN THE WHITBY FORMATION

(UPPER ORDOVICIAN) OF SOUTHERN ONTARIO AND A

BIOSTRATIGRAPHIC FRAMEWORK

Pamela Tuffnell and Rolf Ludvigsen

Department of Geology, University of Toronto, Toronto, Ontario MSS lAl

Manuscript approved for publication by O.L. White, Section Chief, Engineering and Terrain Section, Ontario Geological Survey, Toronto, June 15, 1984. This report is published by permission of V.G. Milne, Director, Ontario Geological Survey.

X!

ABSTRACT

The Whitby Formation in southern Ontario is a 25-80 m 4- sequence of recessive shales of Late Ordovician (Maysvillian) age located between the lindsay Formation below and the Georgian Bay Formation above. The Lower Whitby consists of 10 m i of black and brown bituminous shale; the Upper Whitby consists of 20-70 m 4- of grey shale. Detailed biostratigraphy of these shales have proved difficult because completely exposed sections do not exist and the available outcrops are of low quality. The recent drilling programme initiated by the Ontario Geological Survey opens up a new source of biostratigraphic data for the Whitby Formation. Twenty continuously- cored holes have now been drilled in the Manitoulin, Collingwood, Corbetton, Bolton, Toronto, and Ottawa areas. We sampled seme 1000 m of Whitby core for the olenid trilobite Triarthrus Green and recovered specimens from about 800 levels. Surface sections were also sampled. Four species occur in the Whitby: T. eatoni (Hall), T. canadensis Smith, T. rougensis Parks, and T. spinosus Billings. Taxoncmic revision of these species and logging of occurrences within the Whitby indicate that the four species display largely overlapping stratigraphic ranges. A biostratigraphic framework based on frequency of occurrence of each of the four species is proposed, The distribution of three biostratigraphic units (Faunas A - C) in the Whitby is controlled by both temporal and environmental factors. INTRODUCTICN

The narrow belt of poorly exposed shales which extends from Whitby on Lake Ontario to Collingwood on Georgian Bay was outlined early in the period of geological exploration of Canada West, as was its stratigraphic position between the Trenton limestones below and the Hudson River limestones and elastics above. Logan (1863) recognized the faunal and lithologic similarity of the lower part of these shales with the Utica Shale of central New York State and applied this name to the shales in Canada. The bituminous shales of the lower Utica attracted quick attention by entrepeneurs. Henry Youle Hind of the University of Toronto had suggested the possibility of commercial extraction of "illuminating gas" from these shales as early as 1857 (Morton, 1980). By 1860 commercial operations had commenced at Craigleith, near Collingwood, and Logan (1863, p. 784) reported that 250 gallons of crude oil were distilled daily from 30 to 36 tons of bituminous shale at a cost of 14 cents a gallon. Logan©s Utica Shale in southern Ontario was later divided into a number of formations and members and the stratigraphic terminology had become increasingly complex by the mid 1950©s (see Liberty, 1969, table I for a summary). The distinctive trilobite Triarthrus (Fig. 1) is a unique faunal constituent of these shales and seme investigators, notably W.A. Parks of the University of Toronto, used this trilobite to subdivide this sequence of shales. He (1928) recognized a Triarthrus-bearing interval comprising the Upper Collingwood, Lower Gloucester, and Upper Gloucester (or Blue Mountain) as distinct from Triarthrus-free units below (Lower Collingwood) and above (Dundas). Species were also used in a lithostratigraphic sense. The absence of T. spinosus in the Collingwood area was taken as evidence that the Lower Gloucester was absent here and that the Blue Mountain rested unconformably on the Upper Collingwood (Parks, 1928, p. 60). Parks© Triarthrus-bearing interval was subsequently named the Whitby Formation by Liberty (1969) according to explicit lithologic criteria. In his pioneering contribution, Parks (1928) demonstrated that different portions of the shale succession contain largely distinct associations of Triarthrus species which are useful for correlating the disjunct areas of outcrop of the Whitby Formation. Further biostratigraphic work has been frustrated by the low quality of the outcrops of the Whitby Formation. Completely exposed sections through the formation are unknown, and where portions are exposed, fossil collecting is difficult. Only the bituminous shales of the Lower Whitby are sufficiently compact to survive weathering; the soft grey shales of the Upper Whitby tend to disintegrate into small chips and clay when exposed on the surface. Thus, detailed information on the stratigraphic range of each species of Triarthrus has remained elusive. An opportunity to sample the entire Whitby Formation in a number of areas arose in 1982 when core from the extensive drilling programme initiated by the Ontario Geological Survey became available. The aim of the OGS drilling programme is to outline the thickness, depth, and lithologies of the Whitby Formation in the areas between Lake Ontario and Georgian Bay and on Manitoulin Island and in the Ottawa area (Johnson et al.,1983 Triarthrus is the only fossil which occurs through the formation in most of these areas and, furthermore, it is of an appropriate size to be preserved in the 4.5 cm diameter core. Seme 1000 m of core from the Whitby Formation is now available for study. We have sampled this core for Triarthrus (as well as other trilobites, brachiopods, and graptolites) and have recovered specimens (mainly cranidia) from about 800 levels in twenty drill holes. Shorter surface sections were also sampled in the Toronto, Collingwood, and Manitoulin areas (see Fig. 2, Appendix). In this paper we present the results of a taxonomic revision of the four species of Triarthrus which occur in the Whitby Formation of southern Ontario based on type specimens, museum collections, and on material recovered during the present sampling programme. We have also studied the poorly known type species, Triarthrus beckii Green, from New York State. A tentative Triarthrus biostratigraphy for the Whitby Formation is discussed with reference to the range and the frequency of occurrence of Triarthrus eatoni (Hall) , T. canadensis Smith, T. rougensis Parks, and T. spinosus Billings. SYSTEMATIC PALEONTOLOGY

Terminology. With few exceptions, the terminology follows the Treatise (Moore, 1959) or Henningsmoen (1957, fig. 2). The glabella includes the occipital ring. The lateral glabellar furrows are numbered from the rear (Is, 2s, 3s, and 4s), as are the lateral glabellar lobes (Ip, 2p, 3p). The descriptors length, long, and short refer to sagittal and exsagittal directions and width, wide and narrow refer to transverse direction. Long and short palpebral lobes refer to palpebral lobes longer or shorter than one-third glabellar length. The inflated rim in front of the preglabellar furrow is called the frontal area.

Repositories. All material collected for the present study is kept at the Royal Ontario Museum,- Toronto (ROM.). Other illustrated material is kept at the Geological Survey of Canada, Ottawa (GSC), New York State Museum, Albany (NYSM), and the National Museum of Natural History, Washington (USNM).

Triarthrus Green, 1832

Type species. Triarthrus beckii Green, 1832 from the Snake Hill Formation at Cohoes, New York State (by monotypy).

Triarthrus beckii Green, 1832 PI. l, figs. 1,2, Fig. 3

1832 Triarthrus Beckii Green, p. 87, pi. l, fig. 6. (o

1838 Paradoxides Beckii, Hall, p. 142, fig. 1. 1847 Calymene beckii, Hall, p. 237, pi. 66, figs. 2f, 2g (non pi. 64, figs. 2b, 2c, pi. 66, figs. 2a, 2b, 2d, 2e ^.T. eatoni). 1863 Triarthrus becki, Logan, fig. 200. 1920 (non) Triarthrus becki, Raymond, pis. 1-6 (- T. eatoni). 1924 (non) Triarthrus becki, Foerste, p. 239, pi. 43, fig. 22 (- T. eatoni). 1926 Triarthrus becki, Ruedemann, p. 115, pi. 21, figs. 10-12. 1957 Triarthrus eatoni (Hall), Whittington, p. 941, pi. 116, figs. 1-13. 1979 Triarthrus eatoni, Ross, p. 2, pi. l, figs. 1-13.

Diagnosis. A species of Triarthrus with a barrel-shaped glabella which is rounded anteriorly. Palpebral lobe is short, centred opposite 3p and 4p lobes. Posterior facial suture follows arc of circle to meet margin at right angle. . Free cheek is narrow. Genal angle is evenly rounded. Posterior border of fixed cheek is short. Thoracic segments number 12 to 14. Elliptical pygidium bears 4 axial rings.

Types. Jacob Green distributed plaster casts of the type slab of Triarthrus beckii to a number of institutions. We illustrate the one in the U.S. National Museum of Natural History (USNM 4966, Pi. l, fig. 1). Green©s material comes from "black shaly limestone on the canal near Cohoes falls, in the state of New York". According to Ruedemann (1926, p. 115) this locality is within the Snake Hill Formation which is a silty equivalent of the Utica Shale (Fisher, 1977 f pi. 4).

Remarks. The original type slab of Triarthrus beckii Green, 1832 from Cohoes Falls, New York State has been lost for many years and neither Green©s illustration nor his Latin diagnosis is sufficient to characterize this species. Jacob Green ensured validity of his species and genus by the (then and now) unheard of act of distributing plaster casts of the type slab showing fourteen cranidia (Pi. l, fig. 1) with his monograph on North American trilobites. Hall (1838) was able to distinguish T. beck i i from a new species, T. eatoni; but, in a highly uncharacteristic move, he later (1847, p. 237) concluded that his species is a junior synonym of Green©s (see Prendergast, 1978, for a fascinating account of the true authorship of Hall©s 1838 paper). Hall©s (1847) synonymy stood unchallenged for the next eighty years and, as a result, the celebrated pyritized specimens of Triarthrus from the Utica Shale near Rome, New York State discovered by W.S. Valiant and C.E. Beecher were described under the name of ;r. becki (see Raymond, 1920, p. 39). Ruedemann (1926) re-opened the discussion by concluding that specimens of Triarthrus from the Snake Hill Formation and the Canajoharie Shale differ specifically from specimens from the Utica Shale and the Frankfort Formation. He applied the name T. becki to the former group and T. eatoni to the latter. Ruedemann noted that the two species differ in a number of cranidial features. In comparison with T. eatoni, T. becki has a wider glabella, shorter frontal glabellar lobe, "rounded" glabellar outline, less backwardly-curved lateral glabellar furrows, larger fixed cheeks, and shorter palpebral lobe which is placed farther forwards. The validity of Ruedemann"s cited differences between T. becki and T. eatoni as species discriminating characters was 8 questioned by Cisne et al. (1980) who maintained that the becki and eatoni morphs were both ontogenetic and spatial/temporal variants of a single species, T. becki. Cisne et al., (1980, fig. 2) used two biometric techniques to evaluate variation in T. beckii/eatoni through a 40-80 m thick package of upper Middle Ordovician rocks along a 35 km transect in central New York State. One involved linear measurements of cranidia and the other angular measurements. Neither of these measurements dealt with or quantified the characters that we consider diagnostic of the two species (that is, size of palpebral lobe and position relative to the lateral glabellar furrows, course of posterior facial suture, and shape of glabella). Cisne et al. claimed that, as a result of allometric growth, T. beckii passed from the eatoni to the beckii morph with increasing size. Their documentation is not convincing. They calculated the quadratic equation

WG = 0.88 LG 1 - 11 (r^ 0.986). for glabellar width (WG) and glabellar length (LG) relationships of 395 Triarthrus cranidia from their entire study area. We have calculated the linear equation LG * 1.167 WG - 0.169 (r = 0.968) for 331 Triarthrus cranidia from a one metre section of the lower Whitby Formation (loc. TO 5, Fig. 2). Both of these equations do indeed indicate allometric growth (Gould, 1966, p. 595), but the allometry is so slight that it can be viewed as essentially isometric. According to the data of Cisne et al., the cranidia pass from the eatoni morph (LG greater than WG) to the becki i morph (WG greater than LG) at a glabellar length of 3.5 mm. According to our data, it occurs at a glabellar length of 1.0 mm. However, LG and WG proportions do not distinguish the two species and, in any case, the putative transformation occurs at too small a size to justify the claim by Cisne et al. (1980, p. 53) that the two morphs are ontogenetic variants of the same species. Cisne et al. (1980) used largely angular measurements to document spatial and temporal variations in Triarthrus cranidia. They calculated gamma (the sum of six angular measurements; their Equation 2) as a unidimensional measure of glabellar proportions and claimed that low gamma values characterize the beckii morph and high values the eatoni morph. Gamma values are difficult to evaluate, but apparently they record a combination of breadth of glabella and transverse width of Is and 2s furrows (again, these characters do not differentiate T. beckii from T. eatoni). Although the change of gamma values in a downslope direction (Cisne et al., fig. 7) and in an upsection direction (Cisne et al., fig. 9) is only weakly directed, it does document important spatio-temporal variations. The evidence that these trends are expressed within a single species, T. beckii, is lacking. We suggest that they may be a partial measure of the frequency of occurrence of two contemporaneous species, T. beckii and T. eatoni, at va©rious sites along temporal and environmental gradients. This suggestion, in no way, invalidates the plausible suggestion by Cisne et al. (1980, p. 58) that the replacement of T. beckii by T. eatoni near the base of the Edenian in central New York State )0 is environmentally based rather than temporally based. We return to the arrangement proposed by Hall (1838) and Ruedemann (1926); that is, Triarthrus beckii is a species distinct from T. eatoni and that the diagnostic characters are the shape of the glabella, the position and size of the palpebral lobe, and the course of the posterior facial suture (see Figs. 3, 4).

Occurrences. Common in Snake Hill Formation, lower Utica Shale (= Canajoharie Shale), and other localities in New York State. These occurrences are largely Shermanian. Also present in the Kope Formation of Kentucky (Edenian).

Triarthrus eatoni (Hall, 1838) Pi.l, figs. 3-6, PI. 2, figs. 1-4, Figs. 1,4

1838 Paradoxites Eatoni Hall, p. 142, fig. 2. 1847 Calymene beckii (Green), Hall, p. 237, pi. 64, figs. 2b, 2c, pi. 66, figs. 2a, 2b, 2d, 2e. 1920 Triarthrus becki, Raymond, p. 39, pis. 1-6. 1924 Triarthrus becki, Foerste, p. 240, pi. 43, fig. 22. 1924 Triarthrus eatoni, Foerste, p. 240, pi. 44, fig. 13. 1926 Triarthrus eatoni, Ruedemann, p. 119, pi. 21, figs. 7-9. 1937 Triarthrus eatoni, Kay, pi. 10, unnumbered fig.

1957 (non) Triarthrus eatoni, Whittington, p. 941, pi. 116, figs. 1-13 ^ T. beckii) 1975 Triarthrus eatoni, Cisne pis. l, 2. 1978 Triarthrus eatoni, Ludvigsen, pi. 6 fig. 54. 1979 Triarthrus eaton!, Ludvigsen, figs. 38, 39. 1979 Triarthrus eatoni, Verma, photo 3, pi. l, figs, l, 2.

1979 (non) Triarthrus eatoni, Ross, p. 2, pi. l, figs. 1-13 (- T. beckii) 1981 Triarthrus eatoni, Cisne, pis. 17-23.

Diagnosis. A species of Triarthrus with a semicircular cephalon. Parallel-sided glabella is rounded anteriorly. Palpebral lobe is long, centred opposite 2s furrow. Posterior facial suture diverges at 40-45 0 from an exsagittal line. Free cheek is narrow. Genal angle is evenly rounded. Posterior border on fixed cheek is moderately short. Thoracic segments number 13. Elliptical pygidium bears 4 axial rings.

Types. We have made enquiries at a number of institutions where some of the J. Hall collections are kept in order to determine whether any of their New York specimens of Triarthrus matches the illustrations of T. eatoni in Hall (1838, 1847). These institutions include the New York State Museum, American Museum of Natural History, Field Museum of Natural History, National Museum of Natural History, Department of Paleontology at University of California in Berkeley, Beloit College, Peabody Museum of Natural History, and Milwaukee Public Museum. The enquiries proved unsuccessful. Hall©s (1838, p. 142) original specimens of Paradoxides Eatoni came from "the greywacke slate in Turin, Utica, Fort Plain and elsewhere in the State of New York". We select as neotype the large cranidium from the Utica Shale, Oxtungo Creek, near Fort Plain, New York State that was illustrated by Ruedemann 12. (1926, pi. 21, fig. 8). This specimen (NYSM 9894, PI. 2, fig. 2)

conforms closely to Hall©s original species concept and it was collected from one of the stratigraphic localities noted by Hall in the definitive paper.

Remarks. Triarthrus eatoni differs from T. beckii in the size and position of the palpebral lobes and in the configuration of the fixed cheek behind the eye (see under T. beckii). From the other three species under consideration, T. eatoni differs by lacking occipital, genal, and thoracic spines. It further differs from T. canadensis in having a rounded front margin to the glabella, narrower fixed cheeks behind the eye, shorter posterior borders on the fixed cheeks, and a smaller pygidium with only four axial rings. T. eatoni differs from T. rougensis in having the palpebral lobes located closer to the glabella and slightly farther forward and from T. spinosus in having larger palpebral lobes.

Occurrences. Common in Utica Shale and Frankfort Formation, central New York State. Common in Lower and lower Upper Whitby Formation and rare in upper Upper Whitby Formation of southern Ontario. These occurrences extend from, possibly, Shermanian to high in the Maysvillian.

Triarthrus canadensis Smith, 1861 PI. 2, figs. 5-9, PI. 3, figs. 1,2, Fig. 5 13 1861 Triarthrus canadensis Smith, p. 275, fig. 1. 1921 Triarthrus canadensis, Parks, p. 47, pi. l, figs. 1-4, 10. 1928 Triarthrus canadensis, Parks, p. 90, fig. 27. 1928 Triarthrus glaber Billings, Parks, p. 89, fig. 26. 1928 Triarthrus cf. glaber/canadensis, Parks, p. 90, fig. 28.

Diagnosis. A species of Triarthrus with a transversely suboval cephalon. Forwardly narrowing glabella is transverse anteriorly. Palpebral lobe is long, centred opposite 2s furrow. Posterior facial suture diverges at 55-60 0 from an exsagittal line. Free cheek is wide. Rounded genal angle bears short, stout, rapidly tapering genal spine. Posterior border of fixed cheek is long. Thoracic segments number 13. Elliptical pygidium bears five axial rings and narrow convex border.

Types. The present location of the holotype of T. canadensis (yoked free cheeks described and illustrated by Smith, 1861) is not known. This specimen came from the Utica Slate at Whitby, Ontario. It cannot be located in the collections of the Royal Ontario Museum or the Geological Survey of Canada.

Remarks. Triarthrus canadensis is readily distinguished from all other species by the shape of the glabella, the very wide cheeks resulting in a transversely suboval cephalon, and by the characteristic genal spines. As Parks (1928, p. 90) noted, it is most similar to T. glaber Billings from the Utica Formation at Lac St. Jean, Quebec which has a similar glabellar and cephalic shape, but which lacks genal spines.

Occurrence Common in Lower an^ lower upper Whitby Formation and rare in upper upper Whitby and basal Georgian Bay formations of southern Ontario. These occurrences are Maysvillian and, possibly, earliest Richmondian.

Triarthrus rougensis Parks, 1921 Pi. 3, figs. 3-12, Fig. 5

1921 Triarthrus spinosus rougensis Parks, p. 51, pi. l, figs. 7, 8, 11. 1928 Triarthrus spinosus rougensis, Parks, p. 89, fig. 25. 1928 Triarthrus spinosus narrawayi Parks, p. 89.

Diagnosis. A species of Triarthrus with a semicircular cephalon. Parallel-sided glabella is gently rounded anteriorly. Palpebral lobe is long, centred opposite 2p lobe. Posterior facial suture diverges at 30-35 0 from an exsagittal line. Free cheek is narrow. Long slender genal spine curves backwards from a point just ahead of rounded genal corner. Posterior border of fixed cheek is short. Thoracic segments number 12; 9th bears long median spine. Trapezoidal pygidium bears 4 axial rings.

Types, The holotype is a well-preserved external mould of a complete specimen (ROM 25170) from the Upper Whitby Formation on Rouge River in the Toronto area. It was illustrated by Parks (1921) and herein (Pi. 3, fig. 5).

Remarks In establishing Triarthrus spinosus rougensis, Parks (1921, p. 51) drew attention to the absence of an occipital spine - a feature which clearly differentiates this taxon from T. spinosus Billings. We consider Parks© subspecies to be a distinct species because other cranidial characters set this taxon apart from T. spinosus (notably the size of the palpebral lobes and course of the posterior facial sutures). Parks (1928, p. 89 claimed that T. spinosus narrawayi Parks differs from T. spinosus rougensis solely by the absence of a thoracic spine. He did not document this statement by illustrations. The holotype of T. spinosus narrawayi, illustrated here for the first time (Pi. 3, fig. 3), does not preserve a thoracic spine, but it does show a faint crease which extends backwards from the ninth thoracic segment. We conclude that T. spinosus narrawayi does possess a thoracic spine and consider it to be a junior synonym of T. rougensis.

Occurrences. Common in upper upper Whitby Formation and rare in lower upper Whitby Formation of southern Ontario. These occurrences are Maysvillian. 16 Triarthrus spinosus Billing, 1857 Pi. 4, figs. 1-6, Fig. 7

1857 Triarthrus spinosus Billings, p. 340. 1863 Triarthrus spinosus, Logan, p. 202, fig. 199 1883 Triarthrus spinosus, Ami, p. 88, unnumbered fig., unnumbered pi., 1921 Triarthrus spinosus, Parks, p. 50, unnumbered pi., fig. 9 1926 Triarthrus spinosus, Ruedemann, p. 121, pi. 21, figs. 13-16. 1937 Triarthrus spinosus, Kay, pi. 10, unnumbered fig. 1956 Triarthrus spinosus. Wilson, pi. 5, figs. 3,4 1964 Triarthrus spinosus, Liberty, pi. 5 fig. 5. 1970 Triarthrus spinosus, Norford et al., pi. 4, fig. 23. 1978 Triarthrus spinosus, Ludvigsen, pi. 6, fig. 55. 1979 Triarthrus spinosus, Ludvigsen, fig. 39C.

Diagnosis. A species of Triarthrus with a semicircular cephalon. Parallel-sided glabella is rounded anteriorly. Palpebral lobe is short, centred opposite 2s furrow. Posterior facial suture follows arc of circle to meet margin at obtuse angle. Free cheek is narrow. Long slender genal spine curves backwards from a point well ahead of rounded genal angle. Occipital ring bears long slender median spine. Posterior border of fixed cheek is short. Thoracic segments number 12; 8th, 9th, and 10th bear slender median spines; that on 9th is twice as long as the other two. Trapezoidal pygidium bears four axial rings. 17 )es. The holotype of T* spinosus, a complete specimen first illustrated by Logan (1863, fig. 199) has not been identified with certainty in the type collections of the Geological Survey of Canada. This specimen came from the Utica Slate in Gloucester Township, Carleton County. The collections at the Geological Survey of Canada include an external mould of a complete specimen (GSC 1938a, PI. 4, fig. 2) that was collected by Elkanah Billings (no date) from the Utica Slate, Lot 17 in Gloucester Township, Carleton County. It agrees well with the illustration in Logan (1863) and it may well be the holotype of T. spinosus. On this external mould, the thoracic spine of the eighth segment partly overlaps the succeeding two spines - a possible explanation why Billings (1857) described T. spinosus as having only a single thoracic spine.

Remarks. The presence of an occipital spine makes Triarthrus spinosus an easily identifiable species, but the species can also be distinguished by the presence of small forwardly-located palpebral lobes and by the course of the posterior facial suture. Ami (1883) corrected Billings© (1857) statement that only the eighth thoracic segment of T. spinosus carries a median spine by demonstrating that median spines are present on the eighth, ninth and tenth segments. Our investigation confirms Ami©s conclusion of three thoracic spines, but we have no evidence to support Ruedemann©s (1926, p. 122) contention that T. spinosus has spines on all of the thoracic segments posteriorly of the seventh segment. 19 Occurrences. Common in Whitby Formation of the Ottawa area. Also occurs in upper Utica Shale at Holland Patent, central New York State. These occurrences are Maysvillian.. 19

STRA-nGRAPHIC TERMINOLOGY"

We refer to three formations in the present study: Lindsay, Whitby, and Georgian Bay Formations (Fig. 8). The Whitby Formation is used here as an inclusive term for all the Upper Ordovician shales located between the Lindsay Formation and the Georgian Bay Formation in southern Ontario. Liberty (1969) considered the Collingwood, Gloucester, and Blue Mountain to be biostratigraphic or local names of dubious applicability and assigned these units to his Whitby Formation. He retained the names Eastview and Billings (Wilson, 1946) for the black limestones and shales of the Ottawa area which occupy an identical stratigraphic position as the Whitby Formation on the other side of the Frontenac Axis. We consider that there is no justification for the maintenance of a different stratigraphic termin ology for the Ottawa area and the Whitby Formation, as used herein, includes these two units. The Sheguiandah Formation on Manitoulin Island is clearly identical to the Upper Whitby Formation (see Barnes et al, 1978) and we conclude that the name Sheguiandah is superfluous. Thus, in our usage, the Whitby Formation includes the units previously called Collingwood, Upper Collingwood, Gloucester, Blue Mountain, Sheguiandah, Eastview, and Billings by previous authors. The Georgian Bay Formation conformably overlies the Whitby Formation throughout southern Ontario. It consists of grey carbonates, shales, and siltstones interbedded in variable proportions. Following Liberty (1969), we draw the base at the first limestone interbed above the grey shales of the Upper Whitby. FIELD WORK AND SAMPLING PROGRAiyME

The drilling programme of the Ontario Geological Survey provided critical information on the range of species through the Whitby. The holes were continuously cored and the core recovery was close to lOO©fc. A large number of fossiliferous horizons were identified and sampled, but because the diameter of the core is small only one specimen (rarely two or more) was recovered from each fossiliferous horizon. In order to supplement the biostratigraphic data from the cores, larger collections were made from the limited surface sections available in the Manitoulin, Collingwood, and Toronto areas.

Manitoulin area. The Whitby Formation is exposed along a belt subparallel to the shore line on the north coast of Manitoulin Island. Here, the stratigraphy is complicated by the presence of Precambrian quartzite hills around which limestones of the Trenton Group were deposited. By the Maysvillian when the Whitby was being deposited, these hills were possibly covered. The Upper Whitby was sampled south of Little Current at the junction of Highway 68 and White Point Road (MT 4). A 5 m section of the Lower Whitby is exposed along the river flowing through the Village of Sheguiandah (MT 5). Of the three drill holes on Manitoulin Island, only one (MT 2) penetrated the entire formation. The other two were spudded in the Upper Whitby and continued into the Lindsay

Collingwood area. The shore line of Georgian Bay west of Collingwood exposes excellent sections of the Lower Whitby. The Upper Whitby is intermittently exposed along the streams flowing off Blue Mountain. Two surface sections were measured. The better section (CW 11) extends along the stream which enters Georgian Bay immediately east of Craigleith Provincial Park. A few metres of the Lower Whitby is exposed at lake level and 10 m of the lower part of the Upper Whitby is exposed farther upstream. The contact of the Lower and Upper Whitby is covered at road level. Of the nine holes drilled in the Collingwood area, only one (CW 2) penetrated the entire formation. In this hole, the Lower Whitby is 10 m thick and the Upper Whitby 60 m thick (Fig. 8).

Corbetton and Bolton areas. No adequate surface exposure of the Whitby Formation exists inland between Georgian Bay and Lake Ontario. The entire Whitby was penetrated in the Corbetton hole (CB 1). Here, the section is nearly identical to that encountered in the complete Collingwood hole. At Bolton, the hole was spudded in the Upper Whitby and continued into the Lindsay, (Fig. 8).

Toronto area. Excellent sections of the Lower Whitby are available in artificial exposures close to Lake Ontario at Darlington (TO 5) and at Bowmanville. The exposures of the Lower Whitby along the creek flowing through Oshawa (Liberty, 1969, pi. 26) are now almost completely covered. The Upper Whitby is not well exposed anywhere in the Toronto area. Isolated outcrops on the Little Rouge River (TO 6) were sampled. Three of the four drill holes in the Toronto area were spudded in the Upper Whitby. Only one (TO 4) penetrated the entire formation, but here the upper boundary of the Whitby cannot be specified according to the same criterion used in the Collingwood area, because limestone interbeds are lacking. The boundary interval in this drill hole is a sequence of silty shales (Fig. 8) which appears to be equivalent to the Upper Whitby and the lower part of the Georgian Bay Formation on .Manitoulin Island. In the complete drill hole, the Lower Whitby is about half the thickness of the member in other areas.

Ottawa area. Surface exposures of the Whitby Formation in the Ottawa area are extremely poor. The bulk of the surface data (and fossil collections) was gathered from temporary exposures in foundations for government office buildings. Of the two drill holes, one did not reach the Lower Whitby and the other (OW 2) was spudded in the Upper Whitby and continued through the thick Lower Whitby into the Lindsay. 23

STRATIGRAPHY OF THE WHITBY FORMATION

The Whitby Formation is a southwardly-thickening unit of recessive shales located between the Lindsay Formation and the Georgian Bay Formation in southern Ontario. The thickness of the Whitby increases from less than 30 m in the Manitoulin area to greater than 80 m in the Toronto area. We follow Liberty (1969) in placing the lower boundary of the Whitby at the first black shales or mudstones above the grey lime muds-tones of the Lindsay Formation and the upper boundary at the first impure carbonate "hardband" which defines the base of the Georgian Bay Formation. On the basis of these criteria, the base of the Whitby is either sharply defined or gradational over only a few tens of centimetres, but it has not yet been demonstrated that this level is at exactly the same horizon in all six areas studied. Liberty (1969, p. 68) suggested that the base of the Whitby represents a disconformity; however, the photograph docu menting this relationship (his pi. 24) is of a limestone interbed within the lower Whitby not at the base of the formation which occurs a few metres downsection. We have seen no evidence of erosion or non-deposition at this horizon. Because we follow Liberty©s original definition of the base of the formation, we assign the interval of alternating black shale and limestone in the Collingwood, Corbetton, and Ottawa areas to the Whitby Formation (Fig. 8).

Liberty (1969) recognized three members of the Whitby Formation in the Toronto area which were differentiated mainly on the basis of colour a Lower Member of black shale, a Middle Member of brown shale, and an Upper Member of grey shale. Only the Lower and Upper members were recognized in the Collingwood area, and Liberty (like Parks before him) suggested that the Middle Member was removed by erosion. For this study we recognize only a Lower Whitby C^Tliberty 1 s Lower Member) and an Upper Whitby ^Liberty©s Middle and Upper members) . 24

The Lower Whitby comprises dark brown to black bituminous and calcareous and non-calcareous shales and raudstones with cannon pyrite. Interbedded grey limestones occur in some areas. It maintains a uniform thickness of 10 m over most of the study area, but is somewhat thinner in the Toronto and Manitoulin areas and considerably thicker in the Ottawa area (Fig. 8). The carbonate content of the Lower Whitby shows considerable variation. In the Collingwood area, the Lower Whitby is uniformly calcareous; in the Toronto area, it comprises non-calcareous shale with occasional 1-2 cm bands of calcareous shale; and in the Ottawa area, the Lower Whitby is only slightly calcareous. The Upper Whitby consists of a monotonous sequence of grey and pale brown non- to slightly calcareous shales with rare siltstone and claystone interbeds. In general, the Upper Whitby is less calcareous than the Lower Whitby. In the Toronto and Bolton areas, the boundary interval consists of a 2-5 m section of alternating light grey and dark grey bands. We place the lower boundary of the Upper Whitby at the base of the lowest light grey shale band. The upper boundary of the Whitby Formation is, in all likelihood, older in the Manitoulin area than in the areas to the south. The southward thickening of the Upper Whitby evident in Figure 8 appears to be the combined result of depositional thickening and a facies change of interbedded limestone and shale of the lower Georgian Bay Formation in the Manitoulin area to shales and siltstones of the Upper Whitby in the Toronto area. Lithologically and faunally, the Whitby Formation (particularly, the Lower Whitby) is closely allied to other shale units in eastern North America. These brown bituminous shales and mudstones were deposited in a broad belt from Ontario and Michigan in the south to 25

Southampton Island and Akpatok Island in the north (Ludvigsen, 1979b, fig. 11) as a result of an extensive Late Ordovician transgression. Triarthrus and Pseudogygites are particularly characteristic associates in these shales and Vforkum et al (1976) designates this association the "Iieptobolus-Triarthrus-Pseudogygites-Geisonoceras fauna". BIOSTRATIGRAPHY

A biostratigraphic framework for the Whitby Formation in southern Ontario must be based on a floral or faunal group that has a reasonable chance of being recovered from all parts of the formation in each of the areas. Most macrofossils are intermittently preserved in the Whitby Formation. Cephalopods, graptolites, and brachiopods are encountered occasionally. The trilobite Pseudogygites latimarginatus is common in the Lower Whitby, but has not been recovered from higher parts of the formation (Ludvigsen, 1979b). By contrast, the trilobite Cryptolithus is locally present in the upper part of the Upper Whitby, but has not been recovered in the lower parts of the formation. Little work has been completed on the microfossils of the Whitby. The shales tend to resist acetic acid treatment and, as a result, only few conodonts have been recovered. Barnes et al. (1978) recorded a Maysvillian fauna from the Upper Whitby on Manitoulin Island. Palynomorphs are potentially very useful for detailed biostratigraphy of the Whitby, but to date little work has been attempted. The only macrofossil that is encountered regularly in the Whitby cores is the olenid Triarthrus and, as Parks (1928) demonstrated, this trilobite has considerable biostratigraphic potential for these shales in southern Ontario and in adjoining regions. Parks, however, was limited by having access to only the incomplete surface sections in the Collingwood, Toronto, and Ottawa areas. We improve on Parks© work by determining the complete stratigraphic range of each species in many more sections and by dealing with more rigorously defined taxonomic units. 2.7

A conventional biostratigraphy based on the four species of Triarthrus in terms of assemblage zones, concurrent range zones, or Oppel zones is not feasible for the Whitby Formation because the four species display largely overlapping stratigraphic ranges (Fig. 9). There is, however, a clear differentiation between those parts of the Whitby where a species is densely distributed and those parts where it is rare, and our biostratigraphy attempts to exploit this differentiation. We have chosen to define three biostratigraphic units based on frequency of occurrence of either T. eatoni, T. canadensis, or T^ rougensis-T. spinosus. We emphasize that the distribution of these units within the Whitby is not controlled strictly by time and, therefore, they should not be taken to indicate temporal equivalency. There are undoubtedly a number of (as yet unspecified) environmental variables that exert control on the distribution and the density of occurrence of each of these species.

Fauna A. This biostratigraphic unit is recognized on the basis of frequency of occurrence of Triarthrus eatoni. It corresponds closely to the limits of the bituminous shales of the Lower Whitby in the Collingwood and Toronto areas where it is well expressed in both drill holes (CW 2, TO 2) and in surface sections (CW 11, see Fig. 1; TO 5). Fauna A is not represented in either of the Corbetton and Bolton drill holes and it does not occur on Manitoulin Island where the Lower Whitby belongs to Fauna B. It is either poorly developed or missing in the Ottawa area. Fauna A conforms closely to the interval with abundant Pseudogygites latimarginatus in the lowermost Whitby (Ludvigsen, 1979b). Both T. canadensis and T. rougensis occur sparingly in this fauna. 28

Fauna B. This biostratigraphic unit is recognized on the basis of frequency of occurrence of Triarthrus canadensis. The best representation of this fauna is in the lower part of the Upper Whitby in the drill holes of the Toronto, Bolton, and Corbetton areas where it is distributed over a maximum thickness of 40 m at TO 4. The stratigraphic range of Fauna B thins towards the north-west and it is not recognizable in the drill holes in the Collingwood area. The absence of T. canadensis could be explained by the presence of a disconformity between the Lower and Upper Whitby (as suggested by Parks, 1928) or it may simply be a result of collection failure. This species is known to occur in the lower part of the Upper Whitby in the Collingwood area (Parks, 1928). Fauna B cannot be recognized with certainty in the Ottawa area. Both T. eatoni and T. rougensis occur sparingly in this fauna. Fauna C. This biostratigraphic unit is recognized on the basis of frequency of occurrence of Triarthrus rougensis or T. spinosus. These species have disjunct distributions in Ontario - T. spinosus occurs only in the Ottawa area and T. rougensis only in the Toronto to Manitoulin belt. Based on T. rougensis, this fauna attains its best development in the Toronto and Collingwood drill holes (TO 4, CW 8, CW 2) where it is distributed over a thickness of as much as 30 m. From Collingwood, the stratigraphic range thins towards Manitoulin Island. Based on T. spinosus, Fauna C is present in the upper part of the Lower Whitby in the Ottawa area. Rare specimens of T. eatoni and T. canadensis also occur in Fauna C, as do specimens of Cryptolithus sp. The distribution of the three biostratigraphic units in the Whitby Formation is shown in Figure 10. If there is appreciable time control to the distribution of these faunas, then the Lower Member is slightly younger on Manitoulin Island than in the Collingwood and Toronto areas; and the Lower Whitby in the Ottawa area extends into imich younger strata than in the other areas of southern Ontario. The relationship of Fauna B and Fauna C between the Toronto and Collingwood areas is unresolved. At present, we cannot determine if Fauna B is entirely older than Fauna C and if the apparent absence of Fauna B in the Collingwood area is due to a cryptic disconformity or merely the result of collection failure. We suspect that Triarthrus spinosus and T. rougensis occupy essentially the same level in the Whitby - the former confined to black shales and the latter to grey shales, but it is equally possible that Fauna C in the Ottawa area is somewhat older than Fauna C in the Toronto area. 3O

BIBLIOGRAPHY

Ami, H.M. 1883: Notes on Triarthrus spinosus Billings; Ottawa Field Naturalists Club, Transactions, Vol. l, p. 88-89. Barnes, C.R., Telford, P.G., and Tarrant, G.A. 1978: Ordovician and Silurian conodont biostratigraphy, Manitoulin Island and Bruce Peninsula, Ontario; p. 63-71, in Geology of tne Manitoulin Area, edited by J.T. Sanford and R.E. Mosher, Michigan Basin Geological Society, Special Paper No. 3. Billings, E. 1857: New species of fossils from the Silurian rocks of Canada; Geological Survey of Canada Report of Progress for 1853-1856, p. 340 Cisne, J.L. 1975: Anatomy of Triarthrus and the relationships of the Trilobita; Fossils and Strata, No. 4, p. 45-63. Cisne, J.L. 1981: Triarthrus eatoni (Tnlobita); Anatomy of its exoskeietal, skeletomuscular, and digestive systems; Palaecntographica Americana, Vol. y, p. 99-141. Cisne, J.L., Molenock, J., and Rabe, B.D. 1980: Evolution in a cline: The trilobite ©Iriarthrus along an Ordovician depth gradient; Lethaia, Vol. 13, p. 47-59. Fisher, D.W. ly77: Correlation of the Hadrynian, Cambrian, and Ordovicain rocks in New York State; New York State Museum, Map and Chart Series, No. 25. - 31 -

Foerste, A.F. 1924: Upper Ordovician faunas of Ontario and Quebec; Geological Survey of Canada, Memoir 138, 255p. Green, J. 1832: A monograph of the trilobites of North America? with coloured models of the species; 94p., J. Brano, Philadelpha. Gould, S.J. 1966: Allometry and size in ontogeny and phylogeny; Biological Reviews, Vol. 41, p.587-640. Hall, J. 1838: Descriptions of two species of trilobites belonging to the genus Paradoxides; American Journal of Science, Vol. 33, p.139-142. 1847: Paleontology of New York; Vol. l, 338p., C. Van Benthuysen, Albany Henningsmoen, G. 1957: The trilobite family Olenidae; Skrifter Utgitt av Det Norske Videnskaps-Akademi i Olso 1. Mat-Naturv. Klasse. No. l, 303p. Johnson, M.D., Russell, D.J. and Telford, P.G. 1983a: Shallow drilling results, 1981-82, Oil Shale Assessment Project; Ontario Geological Survey, Open File Report 5458, 36p. 1983b: Drillholes for Regional Correlation 1981-82. Oil Shale Assessment Project; Ontario Geological Survey, Open File Report 5459, 20p. Kay, G.M. 1937: Stratigraphy of the Trenton Group; Bulletin of the Geological Society of America, Vol. 48, p.233-302. Liberty, B.A. 1964: Upper Ordovician stratigraphy of the Toronto area, p.43-53, in Guidebook-Geology of Central Ontario, edited by M.J. Copeland, American Association of Petroleum Geologists and Society of Economic Paleontologists and Mineralogists. -32 -

Liberty, B.A. 1969: Paleozoic Geology of the Lake Simcoe area, Ontario; Geological Survey of Canada, Memoir 355, 201p. Logan, W.E. 1863: Geology of Canada; Geological Survey of Canada, Report of Progress from its commencement of 1863, Montreal, 983p. Ludvigsen, R. 1978: Towards an Ordovician trilobite biostratigraphy of southern Ontario; p.73-84 in Geology of Manitoulin Area, edited by J.T. Sanford and R.E. Mosher, Michigan Basin Geological Society, Special Paper No. 3 1979 Fossils of Ontario, Part 1: The trilobites; Life Sciences, Miscellaneous Publications, Royal Ontario Museum, Toronto, 96p. 1979b The Ordovician trilobite Pseudogygites Kobayashi in eastern and arctic North America; Life Sciences Contributions, Royal Ontario Museum, Toronto, No. 120, 41p. Moore, R.R. (editor) 1959: Treatise on Invertebrate Paleontology, Part O, Arthropoda 1; Geological Society of America and University of Kansas Press, 560p. Moreen, W.L. 19bO: henry Youle Hind 1823-1908; Canadian Biographical Studies, University of Toronto Press. Toronto and Buffalo, 161 p. Noford, B.S., Bolton, T.E., Copeland, M.J., CumttLng, L.M., and Sinclair, G.W. 1970: Ordovician and Silurian faunas; p. 601-613, in Geology and Economic Minerals of Canada, edited by R.J.W. Douglas, Economic Geology Report No. 1. Parks, W.A. 1921: On Triarthrus canadensis, Triarthrus glaber, and Triarthrus spinosus; Transactions of the Royal Society of Canada, 3rd series, Vol. 15, section 4, p. 47-51. Parks, W.A. 1928: Faunas and stratigraphy of the Ordovician black shales and related rocks in southern Ontario; Transactions of the Royal Society of Canada, 3rd series, Vol. 22, section 4, p. 39-92. Prendergast, M.L. i97b: James Ctoight Dana: The life and thought of an American scientist; Unpublished Ph.D. thesis, University of California, Los Angeles. Raymond, P.E. i92u: The appendages, anatomy, and relationships of triiobites; Memoirs of The Connecticut Academy of Arts and Sciences, Vol. 7, 169 p. Ross, R. J. ,Jr. 1979: Additional triiobites from the Ordovician of Kentucky; United States Geological Survey Professional Paper, 1U66-D, p. D1-D13. Kuedemann, R. 19 ly: On some cases of reversion in trilobites; New York State Museum Bulletin No. 227-228, p. /0-/9. Kuedemann, R. 1926: The Utica and Lorraine Formations of New York, part II, Systemic Paleontology, number 2; New York State Museum Bulletin No. 272, 22b p. Smith, J.F. 1861: Note on a new species of Triarthrus from the Utica Slate of Whitby Canada West; Canadian Journal, New Series, Vol. 6, p. 275. Verma, H.M. 1979: Geology and fossils. Craigleith area. Ontario; Ontario Geological Survey Guidebook wo. 7. 61 p. Whittington, H.B. 1957: Ontogeny of E13.iptocephala, Paradoxides, Sao, Blainia, and Triarthrus (Trilobita); Journal of Paleonology, Vol. 31, p. 934-946. Wilson, A.E. 1946: Geology of the Ottawa-St. Lawrence Lcwland, Ontario and Quebec; Geological Survey of Canada, Memoir 241, 6b p. wilson, A.E. 1956: A guide to trie geology of the Ottawa District; Ottawa Field Naturalists Club, Monograph of the Canadian Field Naturalist, Vol. 70, No. i, 68 p. winder, C.G. and Sanford, B.V. iy?2: Stratigraphy and paleontology of the Paleozoic rocks of Southern Ontario; International Geological Congress 24th session, Field Excursion A45-C45, Guidebook. 74 p. Wbrkum, K.H., Bolton, T.E., and Barnes, C.R. 197b: Ordovician geology of Akpatok Island, Oigava Bay, District of Franklin. Canadian Journal of Earth Sciences, Vol. 13, p. 157-178. APPENDIX OF LOCATIONS OF SURFACE AND SUBSURFACE SECTIONS

DH - drill hole, SS - surface section, OGS drill hole name is included in brackets.

Manitoulin Area MT l DH Manitoulin Island, Howland Township, Lot 16, Cone. VI (SIS5). MT 2 DH Manitoulin Island, Sheguindah Township, Lot 27, Cone. X (SIS6). MT 3 DH Manitoulin Island, Howland Township, Lot 23, Cone. VI (SIS7). MT 4 SS Highway 68, south of Little Current, near junction with White Pine Road. MT 5 SS Along river in Sheguindah, from the bay to the road.

Collingwood Area CW l DH Grey County, Collingwood Township, Lot 27, Cone. VII (CLGDl). CW 2 DH Grey County, Collingwood Township, Lot 24, Cone. VIII (CLGD2). CW 3 DH Grey County, Collingwood Township, Lot 26, Cone. VII (CLGD3). CW 4 DH Grey County, Collingwood Township, Lot 25, Cone. IV (CLGD4). CW 5 DH Grey County, Collingwood Township, Lot 25, Cone. IV (CLGD4B). CW 6 DH Grey County, Collingwood Township, Lot 16, Cone. II (CLGD6A) . CW 7 DH Grey County, Collingwood Township, Lot 10, Cone. I (CLGD7A). CW 8 DH Grey County, Collingwood Township, Lot 40, Cone XII (CLGD16). CW 9 DH Grey County, St. Vincent Township, Town of Meaford (CLGD17). CW 10 SS Section along stream which enters bay just east of Camperdown. CW 11 SS Section along stream which enters bay at east end of Craigleith Provincial Park.

Corbetton Area CB l DH Melanchthon Township, Lot 251, Cone. II (Corbetton 1). 37

Bolton Area BO l DH York County, City Township, Lot 21-22, Cone. V (Nobleton 1).

Toronto Area TO l DH York County, Scarborough Township, Rouge Creek Park (SIS1). TO 2 DH Durham County, Pickering County, Lot 16, Cone. Ill (SIS2). TO 3 DH Durham County, Pickering Township, Lot 32, Range II (SIS3). TO 4 DH York County, Metro Toronto Township, Don Valley Brickyards (SIS4-4A). TO 5 SS Darlington Nuclear Power Station site, excavation at west end, TO 6 SS Little Rouge Creek, 2 km north of Highway 401.

Ottawa Area OW l DH Regional Municipality of Ottawa-Carleton, Gloucester Township, Lot A, Cone IV (SIS9) . OW 2 DH Regional Municipality of Ottawa-Car leton, Cumberland Township, Lot 15, Cone. V (SIS10). Figure l A dense concentration of exuviae of Triarthrus eatoni (Rail, 1838) from the lower Whitby Formation at Craigleith, Collingwood area (ROM 35375, X 1.4).

Figure 2 Locality map of southern Ontario showing outcrop pattern of Whitby Formation and location of drill holes and surface sections in the six areas under consideration (Manitoulin, Collingwood, Corbetton, Bolton, Toronto, and Ottawa areas).

Figure 3 Triarthrus beckii Green, 1832. Reconstruction of cranidium, free cheek, and pygidium. Bar represents 5 mm.

Figure 4 Triarthrus eatoni (Hall, 1838). Reconstruction of cranidium, free cheek, and pygidium. Bar represents 5 mm.

Figure 5 Triarthrus canadensis 3nith, 1861. Reconstruction of cranidium, free cheek, and pygidium. Bar represents 5 mm.

Figure 6 Triarthrus rougensis Parks, 1921. Reconstruction of cranidium, free cheek, and pygidium. Bar represents 5 mm.

Figure 7 Triarthrus spinosus Billings, 1857. Reconstruction of cranidium, free cheek, and pygidium. Bar represents 5 mm. Figure 8 The Whitby Formation in southern Ontario as represented by selected drill holes is divided into a lower menber of black bituminous shales and an upper menber of grey shales. Occurrences of four species of Triarthrus (l to 4) are indicated by horizontal bars.

Figure 9 Interpreted ranges of five species of Triarthrus in central New York State and southern Ontario. Solid bars show intervals where species are abundant to cannon; dots show intervals where species are rare.

Figure 10 Distribution of three biostratigraphic units in the Whitby Formation that are defined on the basis of frequency of occurrence of species of Triarthrus. Fauna A - T\ eatoni, Fauna B - T. canadensis, Fauna C T. rougensis and T. spinosus. Stratigraphic base is that shown in Figure 8. 4o

EXPLANATION OF PLATE l

Triarthrus beckii Green, 1832 1. Plaster cast of slab of syntypes distributed by Green (1832), Snake Hill Formation, Cohoes Falls, New York State (illustrated by Ruedemann, 1926, pi. 21, fig. 10), USNM 4966, X 2. 2. Three cranidia, lower Utica Shale ^ Canajoharie Shale, Rouses Point, New York State (illustrated by Ruedemann, 1926, pi. 21, fig. 12), NYSM 9892, X 4.5.

Triarthrus eatoni (Hall, 1838) 3. Small cranidium, Whitby Formation, loc. TO 5, 0.8 m from base, ROM 43101, X 13. 4. Small cranidium, Whitby Formation, loc. TO 5, 0.8 m from base, RDM 43102, X 13. 5. Cranidium, Whitby Formation, loc. TO 5, 0.3 m from base, ROM 43103, X 5.5.

6. Nearly complete exoskeleton, lower Utica Shale, Oxtungo Creek near Fort Plain, New York State (illustrated by

Ruedemann, 1926, pi. 21, fig. 9), USNM 23587, X 2. EXPLANATION OF PIATE 2

Triarthrus eaton! (Hall, 1838) 1. Complete exoskeleton, lower Whitby Formation, Craigleith, ROM 34505, X 4.5. 2. Large cranidium, Neotype (here selected), Utica Shale, Oxtungo Creek near Fort Plain, New York State (illustrated by Ruedemann, 1926, pi. 21, fig. 8), NYSM 9894, X 4.5. 3. Cranidium, Whitby Formation, loc. TO 3, 7.3 m from base, RCM 43104, X 4.5. 4. Complete cephalon, Whitby Formation, loc. OW 2, 9.0 m from base, ROM 43105, X 4.5.

Triarthrus canadensis Smith, 1861 5. Yoked cheeks, Whitby Formation, loc. TO 4, 23.4 m from base, RCM 43106, X 4.5. 6. Cranidium, Whitby Formation, loc. TO 3, 10.3 m from base, RCM 43107, X 4.5. 7. Nearly complete exoskeleton, upper Whitby Formation, Rouge River, l km above Kingston Road Bridge, Toronto (illustrated by Parks, 1921, pi. l, fig. 2), ROM 25188, X 4.5. 8. Large cranidium, Whitby Formation, Ice. TO 3, 19.0 m above base, RCM 43108, X 4.5. 9. Large pygidium, Whitby Formation, loc. TO 4, 23.3 m above base, ROM 43109, X 4.5. EXPLANATION OF PLATE 3

Triarthrus canadensis Smith, 1861 1. Large cranidium, Whitby Formation, loc. TO 3, 9.0 m above base, ROM 43110, X 4.5. 2. Pygidium, Whitby Formation, loc. CB l, 14.7 m above base, RCM 43111. X 4.5.

Triarthrus rougensis Parks, 1921 3. Nearly complete exoskeleton, Whitby Formation, Billings Bridge, Ottawa (previously unf igured holotype of Triarthrus spinosus narrawayi Parks, 1928), ROM 18802, X 2. 4. Cranidium, Whitby Formation, loc. BO l, 27.7 m above base, ROM 43112. X 4.5. 5. Latex impression of complete exoskeleton, Holotype, upper Whitby Formation, Rouge River, l km above Kingston Road Bridge, Toronto (illustrated by Parks, 1921, pi. l, fig. 8), ROM 25170, X 5.5. 6. Cranidium, Whitby Formation, loc. TO 4, 1.0 m above base, ROM 43113. X 4.5. 7. Pygidium, Paratype, upper Whitby Formation, Rouge River, l tan above Kingston Road Bridge, Toronto (illustrated by Parks, 1921, pi. l, fig. 11), ROM 25189, X 5.5. 8. Latex impression of nearly complete exoskeleton, Whitby Formation, loc. MT 2, 14.0 m above base, RCM 43114, X 5.5. 9. Cranidium, Paratype, upper Whitby Formation, Rouge River, l km above Kingston Road Bridge, Toronto (illustrated by Parks, 1921, pi. l, fig. 7), RCM 25171, X 4.5. 10. Large cranidium, Whitby Formation, Ice. BO l, 10.5 m above base, ROM 43115, X 4.5. 11. Free cheek, Whitby Formation, loc. CW 7, 22.0 m above base, RCM 43116, X 4.5. 12. Nearly complete exoskeleton with displaced yoked cheeks, Whitby Formation, Ottawa, GSC 70985, X 3.0. EXPLANATION GF ELATE 4

Triarthrus spinosus Billings, 1857 1. Exoskeleton with displaced yoked cheeks, upper Utica Shale, Holland Patent, New York State (illustrated by Kuedemann, 1926, pi. 21, fig. 14), NYSM 9898, X 4.5. 2. External mould of nearly complete exoskeleton, possibly the Holotype (see text), Whitby Formation, Rideau River, Lot 17, Gloucester Township, Carleton County, Ottawa, GSC 1938a, X 8.2. 3. Cranidium, Whitby Formation, Gloucester Township, Ottawa, GSC 13616, X 5. 4. Incomplete exoskeleton, Whitby Formation, Gloucester Township, Ottawa, GSC 70986, X 3.0. 5. Complete exoskeleton, laterally compressed, Whitby Formation, Gloucester Township, Ottawa (illustrated by Ruedemann, 1919, text-fig. 8), USNM 96235a, X 3.0. 6. Nearly complete exoskeleton, Whitby Formation, Cummings Bridge, Ottawa (possibly the original of Ami, 1883, unnumbered fig.), GSC 1936, X 3.0.

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