reality widely divergent. In his report of 1861 (p. 79) Winchell, relying upon the evidence of Billings and Hall says: "In this state of the case we shall be constrained for the present to regard the Huron Group of Michigan, extending from the conglomerate above the gritstones of Huron county, to the top of the argillaceous limestones of Partridge Point, as probably representing the rocks of the Portage Group of New York." In a paper read before the Geological Society of America, in December, 1893, Brumell, of the Canadian Geological Survey, still refers this shale series to the Portage, but in his table includes the Chemung.* According to the later publications of the Ohio Geological Survey, Newberry did not sharply separate his Huron shale, from his Erie and Cleveland above it and in 1873 he reports the occurrence of diagnostic Portage fossils in the Huron, or lowest member of our St. Clair shale. In his chart of geological time, however, he drops the Huron shale to the level of the Genesee. In the Erie he found positive palæontological proof of its equivalency with the Chemung (p. 164). Three years later Rominger referred the entire series to the Genesee. In a little table of the divisions of the Devonian system published in 1886 (Geological Studies, p. 389), Winchell makes the Erie shale of Ohio the equiva lent of the Portage and Chemung. The Huron shale he correlates. with the Genesee and all together comprise his Huron group. This view harmonizes the apparently discordant views of the various workers and was accepted by Orton. In his report of 1893, he says.§ "The Ohio shale, as Newberry first proved, is certainly the equivalent in the general scale of the Genesee slate, the Portage group, and the Chemung group, the last named being itself a formation of great thickness and extent in New York and Pennsylvania. In other words, the shales of our column fill the entire interval between the Hamilton proper and the Catskill group, and in the judg ment of some geologists a wider interval than that named above." In a paper upon the Devonian system in Canada, published in October, 1899, Whiteaves accepts the Genesee equivalency of the black shale found at Kettle Point, Lake Huron.¶ In the light of our present knowledge then, the 70-80 feet of the shale, found in the northwestern corner of Monroe County, belongs largely, if not entirely, with the Genesee shale of New York. *Bull. Geol. Soc. Vol. IV, 1893, p. 227. § 11. Lithological history. The materials of which these shales are composed were accumulated in the off-shore region of the ocean, or some great inland sea. The fineness of the particles indicates that this region was somewhat remote from the land, yet near enough to receive from it, through the agency of waves and currents, the materials resulting from the erosive agencies continually at work. Deposits of such thickness could probably only have been formed over a slowly subsiding sea bottom. Conditions were not favorable for the ordinary forms of marine animals, such as the corals, mollusca, echinoderms and crustacea, and hence the beds are relatively free from the lime carbonate which these forms secrete from the water. The presence of so much bituminous matter indicates that marine vegetation, of a certain type, was very abundant. This bituminous constitutent of the shale is due very largely to the presence of enormous numbers of minute disc-like bodies, with thick carbonaceous walls. These were discovered by Dawson in the shales of Kettle Point, Lake Huron and described by him in 1871, under the name Sporangites Huronensis.* According to Orton, however, they had been seen previously by B. W. Thomas in the water and clays of Lake Michigan. They are about .01 of an inch in diameter and under the microscope show a papillose exterior, with an attachment scar on one side and a more or less elongated gaping slit upon the other. Remains of Calamites and Lepidodendron were found in association and Dawson regarded them as spore-cases of the latter tree. Without having seen this article by Dawson, in 1882, Orton described these bodies in the above mentioned journal, as spore-cases, containing both macrospores and miscrospores. In August, 1883, Dawson read a paper before the American Association for the Advancement of Science, entitled "On Rhizocarps in the Palæozoic Period." From material furnished by Derby from Brazil two new species were described, S. Braziliensis and S. bilobatus. The spore-cases showed the macrospores in position, so much resembling those of the floating fern of the European rivers, Salvinia natans, that the generic name Protosalvinia was suggested. His former Sporangites Huronensis he considered as the macrospores of related plants, but with their envelopes lost. A similar interpretation is put upon the forms by Clarke who found *American Journal of Science, 3d Series, Vol. I, pp. 256-263. + A Source of the bituminous matter in the Devonian and Sub-Carboniferous Black Shales of Ohio, Am. J. S., 3d Series, Vol. XXIV, pp. 171-174. Proceedings, 1883, pp. 260-264. them abundant in the Marcellus shale of Ontario county, New York. They are associated with immense numbers of minute sub-spherical bodies, regarded as the microspores. These later discoveries are in entire harmony with the view early advanced by Newberry in his Ohio report for 1873, page 156. He there calls attention to the difficulty in conceiving of such widespread shallow water conditions, capable of furnishing the necessary shore vegetation, with the evidence of the proximity of the shore so completely wanting. He referred the bituminous matter to former floating plants and imagined the entire area of the black shales to have been one great "Sargasso sea." Fragments of rushes and trees were occasionally drifted seaward by the same current which distributed the sediments themselves. About such fragments, or the bones and teeth of the terrible fish which inhabited these waters, concretions formed, while the mud was still soft. Later great beds of sediment were superposed, the weight of which compressed the soft material to probably but one-half its original volume, forced out the excess of water and produced the crisp, fissile shale. The pyrite and marcasite were formed wherever soluble sulphates came in contact with putrefying organic matter and oxide of iron, as shown by Bischof many years ago and later by Forchhammer. The sulphates may be derived from the organic matter itself or be in solution in the sea-water in which it is immersed. When sea weeds and iron oxide are in contact double decomposition ensues and the above sulphides of iron result. Forchhammer mentions a beautiful illustration of this action on the western shore of the island of Bornholm where Fucus vesiculosus is very abundant, and all the pebbles on the bottom are coated with a yellow coating of pyrite. Upon exposure, however, it is converted into a sulphate of iron. The author concludes with the following clear statement, "Thus it follows, that wherever putrifying sea-weeds come in contact with ferruginous clay, iron pyrites must be formed, which penetrates the clay, and on weathering first forms sulphate of iron, and if no lime be present, will ultimately, by a new decomposition, change into sulphate of alumina."‡ *On Devonian Spores. American Journal of Science, 3d Series, Vol. XXIX, 1885, pp. 284-289. It should be said, however, that the presence of rock salt in the St. Clair formation, beneath Bay City, indicates other conditions than those of an open sea. British Association for the Advancement of Science, 1844, pp. 155-169. C. Traverse (Hamilton) Group. § 12. Name and geological position. To the beds of soft shale and limestone, which lie conformably: beneath the St. Clair, the term Hamilton was applied by Winchell in his First Biennial Report. Later, to the same series, the name Little Traverse was applied by the same author. In 1895, Lane suggested the name Traverse alone, since the beds occur in the Grand Traverse as well as the Little Traverse region of Lake Michigan. Rominger used the name Hamilton in describing these Michigan beds and for their equivalents in Ohio the same was used by Newberry. For one member of the group, apparently the only representative in Ohio, Orton retains the name Olentangy shale, a name first suggested by N. H. Winchell for a bed of shale exposed in Delaware County. Hamilton has been very generally, if not uniformly, employed for this series by the Canadian geologists who have worked in the adjoining territory of Ontario. Whatever the name, all workers are agreed from the geological position of the beds, their lithological characters, and their numerous and beautifully preserved fossils, that they are the western representatives of the Hamilton of New York, lying between the Marcellus and Genesee shales.* An inspection of Plate I, shows that this group covers the northwestern corner of Dundee, nearly the whole of Milan and the northwest half of London townships. It enters from Lenawee County, extends northeastward as a belt from five to six miles wide and continues into Washtenaw and Wayne counties. Its apparent breadth is increased by the topography of its upper surface, for it and the St. Clair shales have been considerably eroded, as shown upon Plate VI. In the lower section, taken along the line of the Toledo and Ann Arbor railroad, at the left hand the Hamilton beds are designated as limestone and shale. They are seen to have been cut to a level below that of Lake Erie, which results in considerably increasing the breadth of the outcrop beneath the drift. The thickness of this overlying drift increases quite regularly, in consequence, from about 45 feet at the southeastern corner of Milan township, to about 150 feet, just southwest of the village. The actual elevation, above *I used the name Traverse to include Hamilton and Marcellus, and so did Winchell, in which usage it would be practically equivalent to Erian in the sense suggested by Clarke and Schuchert, L. tide, of the surface varies from 636 feet in the northwestern part of Dundee township to 549 feet, where the drift is heaviest southwest of Milan. The dip of the beds is the same in direction and amount as that given for the St. Clair. There are no known exposures of these beds in this section of Michigan, or in any adjoining locality in either Ohio, or Ontario. § 14. Thickness. From well records in northwestern Ohio and southeastern Michigan the Traverse group is known to be rather weakly developed, but to thicken to the north and east. The greatest development known in Ohio is but 20-30 feet according to Orton and in many regions it is not developed at all, the St. Clair then resting upon the underlying Dundee (Corniferous). In his map of the geology of the southern peninsula, published in 1876, Rominger does not represent the Hamil ton at all in the southern portion of the state. In the deep well at Adrian there are 95 feet of limestone and shale which may properly be referred to the Traverse. At Ann Arbor, in the court-yard well, 70 feet of bluish limestone with some clay, were penetrated by the drill, probably without reaching the bottom of the series. This is regarded by Lane as Traverse, by Rominger as Upper Helderberg (Corniferous) and by Winchell as both, in part. At Royal Oak 215 feet of limestone and shale are referred to the Traverse. On the St. Clair river the total thickness is 300 feet. Eastward in Ontario, at Oil Springs, the group is 240 feet, at Petrolea 296 feet and at Kingstone's mills 396 feet in thickness. About Alpena it has increased to 600 feet, according to estimates of Rominger. Within the limits. of Monroe County the bed has not been completely penetrated and we have no reliable data from which to determine its thickness. It is probably, however, not far from 100 feet, judging from the dip of the rocks and the apparent outcrop and surface topography of the beds. This estimate agrees also with the thickness found at Adrian. § 15. Lithological characters. In the typical regions of west central New York the Hamilton beds consist of soft, bluish calcareous shales, with a few thin layers of bluish to gray limestones; the principal one of which is the so called "Encrinal limestone," scarcely more than a foot in thickness, but remarkably persistent. The shales break into coarse, lumpy fragments, not particularly fissile, never crisp and elastic as are the Genesee just above. When struck they seem dull and dead and when |