GEOLOGICAL SOCIETY.

[Continued from p. 467.]

May 6, 1857.-Colonel Portlock, R.E., President, in the Chair. "The Silurian Rocks and Fossils of Norway, described by M. Theodor Kjerulf, and those of the Baltic Provinces of Russia, by Prof. Schmidt, compared with their British Equivalents." By Sir R. I. Murchison, V.P.G.S. &c.

M. Kjerulf of Christiania, having communicated to the author descriptive letters and illustrative diagrams of the relations and dimensions of the different strata of the Silurian rocks of the territory of Christiania, as well as a series of their organic remains,—and Count Keyserling having forwarded to him a memoir by Prof. F. Schmidt, of Dorpat, comprising the results of an examination of the Silurian rocks of the territory of Esthonia, Northern Livonia, and the Isle of Oesel,-Sir Roderick in this paper brought an outline of these documents under the consideration of the Society, in order to show how independent observers in other tracts have come to the conclusion that the Silurian System as defined by them, as well as by himself, forms a natural-history group, both as to its geological relations and its zoological contents. He pointed out also that the Silurian rocks of Russia and Scandinavia agree with those of Britain from the Lingula-flags upwards to the Ludlow rocks inclusive.

M. Kjerulf divides the whole Silurian series of his country into three physical groups, viz. (in ascending order) the Oslo, the Oscarskal, and the Malmoe groups; and in these he recognizes fourteen subdivisions. The lowest, or Lower Oslo group, including the alum-schists with bituminous limestone, and resting upon unfossiliferous quartzites, the equivalent of the Longmynd rocks, represents (though only 150 feet thick) the "primordial zone" of Barrande, and the Lingula-flags and Stiper-stones of Britain. It contains the Graptopora flabelliformis and Fenestrella socialis mixed with Lingulæ, as in Britain; and with these occur the Agnostus pisiformis, Didymograpsus geminus, and Orthis calligramma, which in the Silurian region of Britain are found in the true Llandeilo group. Hence, the author observes, that, in extending our survey, it is impracticable in general classification to separate the Lingula-flags or primordiale" from the Lower Silurian rocks. The Upper Oslo group, with graptolites and orthoceratites, represents the Llandeilo rocks. The Lower Oscarskal groups are referred to the true Caradoc or Bala series, as now defined. The Upper Oscarskal and part of the Lower Malmoe group (comprising the Pentamerus rocks) represent the Llandovery rocks of South Wales, forming a transition from the Lower to the Upper Silurian rocks of Murchison. The equivalents of the Wenlock and Lower Ludlow rocks succeed in the Middle and Upper members of the Malmoe group.

zone

The Silurian rocks of the Baltic provinces of Russia (as indicated in a map) are represented by Prof. Schmidt as consisting essentially of a series of strata following each other in ascending order, at slight angles of inclination to the south, constituting zones trending generally from east to west, and passing under the Devonian rocks of

Southern Livonia. With but partial exceptions the Silurian series of Esthonia is almost entirely composed of calcareous bands.

The "Pleta," or the oldest and most northern group of the series, caps the cliffs of the Gulf of Bothnia, which are known as the "Glint," and is based on the Ungulite grit and associated argillaceous and sandy beds of the government of St. Petersburg. It is of the age of the Llandeilo rocks, and is succeeded by coralline limestones of the Caradoc or Bala age. The next series of strata comprise two bands of Pentameri (P. borealis and P. oblongus), representing the Llandovery series. The succeeding group is developed partly on the continent and partly on the north-eastern portion of the Isle of Oesel, and chiefly consists of dolomites of the Wenlock age. In the south-western portion of the island are still higher strata of the Ludlow series, in which fish-remains are not unfrequent.

In comparing these Scandinavian, Esthonian, and British Silurian rocks together, Sir Roderick particularly dwelt upon-1. the natural indivisibility of the alum-schists and Lingula-flags from the rest of the Lower Silurian series; 2. the extensive occurrence of the Pentamerus-zone, marking the passage-beds between the Upper and Lower members of the series; 3. the general uniformity in the distribution of the organic remains of the several successional groups of beds, although the strata themselves are very variously developed, as to mineral character and thickness; and 4. the characteristic agreement in fossils between the several Silurian areas of Northern Europe, North America, Canada, and the Arctic regions, on the one hand; whilst, on the other, the Silurian rocks of France, Spain, Bohemia, the Ural, and probably of South America, are dissimilar as a group, from their northern representatives, both in palæontological and lithological characters, marking the existence of distinct geographical limits of life during the older paleozoic period.

In conclusion, the author stated that all the evidence tended to prove that in Scandinavia, as in Russia in Europe, the Silurian rocks, both Lower and Upper, form a united and unbroken whole; and that, both by fossils and by strata, they exhibit in those countries, and in a very small compass, a natural-history system quite as complete and more easily understood than their much more expanded, highly varied, and dislocated equivalents in the British Isles.

May 20, 1857.-Col. Portlock, R.E., President, in the Chair. The following communications were read:

1. "Description of a small Lophiodont Mammal (Pliolophus vulpiceps, Owen) from the London clay, near Harwich." By Prof. Owen, F.R.S., F.G.S. &c.

The subject of this paper was a considerable portion of the skeleton of a small quadruped, about the size of a fox, imbedded in, and apparently the nucleus of, one of the septarian nodules of the London clay, which are dredged up at the mouth of the Thames for the purpose of the manufacture of Roman cement.

From this nodule were extricated the skull with the entire series of teeth in both jaws, the right humerus, portions of the pelvis, right femur, left femur, left tibia, and the three metatarsals of a

hind foot. Many portions of ribs and vertebræ remained imbedded in the hard matrix.

The septarian nodule containing the above parts was transmitted to the author by the Rev. Richard Bull, M.A., Vicar of Harwich, by whose permission the bones were extricated, described, and figured for the present communication.

The length of the skull is 4 inches, its extreme breadth 2 inches 2 lines, the height of the cranium opposite the first premolar tooth 9 lines. Its shape and characteristics determine the hoofed nature of this species and its affinities to the Perissodactyla, or the order of Ungulata with toes in odd number.

3-3

C

3-3

The orbit, 9 lines in vertical diameter, is smaller than in the Hyracotherium, and is not situated so low down as in that animal, the Palæotherium, and the Tapir. The dentition accords with the type of the diphyodont Mammalia, viz. i3 3-3=44. The characters of these teeth were described. The canines are small in both jaws: they are separated by a vacant space from the outer incisors, and by a longer interval from the first premolars. These form a continuous series with the remaining teeth in the upper jaw, but are separated by a space of about half their breadth from the second premolar in the lower jaw. The succeeding teeth increase in size to the penultimate molar in the upper, and to the last molar in the lower jaw, which tooth has a third lobe.

In his comparisons of the modifications of the grinding surface of the teeth, the author remarked that the generic or family type of the Lophiodont upper molars is, to have the outer wall developed into two cones, from each of which is continued an oblique ridge which expands into, or joins, a smaller and lower cone on the inner side of the crown.

In Pachynolophus, a subgenus of Lophiodonts founded by M. Pomel, on a species of the size of the Pliolophus from the calcaire grossier of Passy near Paris, the oblique ridges are lower at their commencement and more partially expanded in their course inward than in Lophiodon proper. In Pliolophus the partial expansion is more circumscribed, and forms a small intermediate tubercle, except on the ridge at the hinder half of the last upper molar. In the lower jaw of Pachynolophus the first premolar, according to the description and figure given by M. Gervais (Paléontologie Française, 4to, pl. 17, figs. 1 & 2), is not developed, and the canine is separated from the molar series by a diastema of twice the length of that in Pliolophus. This latter genus, therefore, is more nearly allied, in respect of the number and position of its teeth, to Lophiodon proper; but it differs from all previously known Lophiodonts in the modification of the grinding surface of the molars of the lower jaw. This surface in Lophiodon, Pachynolophus, Lophiotherium, Tapirulus, and Coryphodon presents two transverse ridges connected by a diagonal ridge: whereas each transverse ridge in Pliolophus is divided into a distinct cone, the anterior pair on the second true molar being separated by an intermediate small cone, thus affording, as in the Stereognathus, an instance of three cones on the same transverse line in a lower molar tooth. In the last true molar the anterior pair of cones are united by a low and

short transverse bar-the rudiment of the middle tubercle in the preceding tooth. In Coryphodon the sinking of the middle of each transverse ridge seems a step towards the more complete bifurcation of the ridge in Pliolophus.

The mandible and lower molar teeth of the Hyracotherium are unknown; but, in regard to the upper molars, Pliolophus approaches Hyracotherium in the characters by which it deviates from other Lophiodonts.

The differences in the dentition, and in the part of the skull of the Hyracotherium which can be compared, between that genus and Pliolophus were pointed out in detail; but the degree of resemblance is such as to lead the author to adopt the idea, first broached by the late Mr. W. H. Turner*, that Hyracotherium is more nearly or essentially allied to Lophiodon than to Charopotamus. The third trochanter on the femur of Pliolophus, and the association of three metatarsals in one portion of the matrix, as if belonging to the same hind foot, confirm the essentially perissodactyle affinities of that genus as shown by the skull and teeth. Pliolophus and Hyracotherium form, in the author's opinion, a well-marked section in the Lophiodont family, which seems to have preceded the Palæotherian family in the order of appearance, and to have retained more of the general ungulate type than that family. This is shown by the graduation of the tapiroid modification of the molar teeth into one more nearly resembling that of the Anthracotheria and Charopotami; by the absence of the postero-internal cone on the ultimate premolar, by which all the premolars are, as in Artiodactyles, less complex than the true molars ; by the form and position of the nasal bones and the structure of the external nostril.

In regard to the evidence of closer adherence to type shown by the dentition of Pliolophus and other ancient mammals, the author concluded by remarking that the dental formula of the Oolitic genera Thylacotherium, Spalacotherium, and Triconodon accords, by the unusual number of small and similarly shaped molars, with a less specialized type than that of the Diphyodont Mammalia, which he terms the more general vertebrate type, and exemplifies that which is shown by Reptiles, Fishes, Cetacea, and certain Armadillos: if the Plagiaulax of the Purbeck beds departs from this type in the reduction of its true molars to two, it singularly manifests its closer adherence to the type-dentition of its order by having its peculiarly shaped premolars in the typical number three; whereas the only existing marsupial genus with premolars of such a shape, viz. Hypsiprymnus, Illig., has those teeth reduced to one in each molar series.

The exception offered by the Plagiaular is like that of Proteles amongst the Canide, in which wild species of Dog the true molars are reduced to one in each series. But this exception does not invalidate the generalization from the dentition in the rest of the Dog-and-Wolf family, any more than Plagiaulax affects the general expression of the facts presented by the dentition of the great majority of the known eocene Mammalia, of which the author in conclusion cited thirty-seven genera which exhibited the typical * Annals and Magazine of Natural History, Dec. 1850, p. 397.

diphyodont dentition; some of these genera being strictly carnivorous, some herbivorous, and others omnivorous.

[Professor Owen's paper was illustrated by the unique specimen of the Pliolophus, carefully divested of its matrix; and by highly finished drawings of its dental structure.]

2. "On some Remains of Terrestrial Plants in the Old Red Sandstone of Caithness." By J. W. Salter, Esq., F.G.S.

An extensive series of plant-remains from the Devonian series of the North of Scotland have been made by Messrs. J. Miller and R. Dick of Thurso, by Mr. Peach of Wick, and by Dr. Hamilton in Orkney; and, a comprehensive series having been submitted to the Director-General of the Geological Survey, Mr. Salter offered the present communication to incite Botanists to a more critical examination of this old flora. The fossils occur in a dark-grey flagstone, which is often marked with impressions of Annelide-burrows in pairs. Most of the specimens consist of glossy black coaly matter, either in large compressed stem-like fragments, sometimes 3 feet long and 4 inches broad; or in equally long, but narrower, curved, and occasionally branched forms, which the author regards with some doubt as roots. The stem-like specimens are delicately fluted, but not traversed by joints; and their microscopic structure is similar to that of coniferous wood, especially of the Araucaria. The bituminous substance of these plant-remains is obliquely and closely cleaved, the fissures being often filled up with siliceous matter. In form these fossils resemble some specimens (Aporoxylon) from the Upper Devonian rocks of Thuringia, discovered by Richter, and lately figured and described by Unger.

There are also some smaller, tapering, and branched specimens, which appear to be branchlets of the same trees that have afforded the stems and roots above noticed; and some still smaller branched specimens, bearing occasional tubercles on the branchlets, are regarded by the author as the smaller roots of these trees, and representing the tubercular rootlets of many of the existing Coniferæ.

A new species of Lycopodites (L. Milleri) was also described; and some specimens of Lepidodendron were referred with hesitation to Unger's L. nothum (Transact. Vienna Acad. 1856).

The strata from which these plants were obtained form part of the Middle Old Red group of Sedgwick and Murchison, and of the Lower Old Red of Hugh Miller. Dipterus, Diplopterus, and Asterolepis are the prevailing genera of fish that accompany the plants.

LXX. Intelligence and Miscellaneous Articles.

ON THE VELOCITY OF SOUND IN SOLIDS, LIQUIDS, AND ELASTIC FLUIDS, AND ON THE CORRELATION OF THE PHYSICAL PROPERTIES OF BODIES.-FIRST PART. BY A. MASSON.

GEOM

EOMETRICIANS have summed up the principal physical properties of bodies in a single formula, which expresses the velocity of sound. Although the laws which they have found have not always been confirmed by experiment, they may be regarded as a