or seventy new or partly described species have been found peculiar to this region, and these wait for description. That the additions to the geology of St. David's during the last few years may be more clearly understood, it is well to state what formations are now known to be present in the promontory that forms the north shore of St. Bride's Bay. The Survey Map does not profess to subdivide the slate-rocks and volcanic grits, but only to separate these as a mass from the purple and grey sandstones coloured as Cambrian rock (the Harlech group of Professor Sedgwick). In ascending order we have then : 1. The Harlech Group (Sedgwick), consisting of purple and greenish-grey sandstone, passing above into grey sandstones (not grits) which are fossiliferous. This mass of purple and greenish-grey flags forms the axis of the promontory, thrown into a violent anticlinal along the line of the so-called syenite," which is partly altered Cambrian rock, and partly crystalline rock, perhaps syenite in some places. 66 2. The Menevian Group, 1500 or 1600 feet thick, of dark-grey (and even black) flags and shales, alternating in its upper and larger portion with sandstone. This is the great fossiliferous group. 3. Ffestiniog Group (Sedgwick).-Hard siliceous sandstone with grey flaky slate, containing Lingulella Davisi. 4. Tremadoc Group.-Sandstones and earthy slates, much like those of the Ffestiniog group, but of a bluish-grey colour and more uniform texture. 5. Arenig or Skiddaw Group.-A thick series of iron-stained slates and flags, interlined throughout by felspar lines and felspathic ashes, containing large Trilobites and shells of new species, and Graptolites like those of Skiddaw. 6. Llandeilo Flags.—Black slates, with felspar beds and interbedded trap, fossils abundant. We may now give a few explanatory details, as brief as possible, respecting each of those formations: 1. Concerning the Harlech group, it must be noted that the sections on the south coast (Caerbwddy for instance) show a distinct passage downwards into the central syenitic mass, so gradual as to induce the belief that the mass of rock is no other throughout than altered Cambrian beds. Near St. David's the same thing is visible. Altered purple beds close to the town are succeeded by rock apparently crystalline, but showing distinct rounded grains of quartz (as minute pebbles) throughout the mass. It is evidently a slightly altered grit or conglomerate. In other places further east, the rock is certainly melted in its central portions, but passes so gradually into olive shales through hardened flinty beds and hornstones, that no true boundary can be traced. The series of sandstones, purple, green, and grey, which succeed are laid down with tolerable accuracy on the Survey Map (except where bounded by the prevailing faults). All the accessible localities have been searched for fossils, but with no success until the highest portion was reached; immediately above the topmost purple bands, 160 feet or so of these top beds contains fossils, not many species, but of the genera Paradoxides, Conocoryphe, Agnostus, Theca, and a new genus, Cyrtotheca. These are of much the same character as those of the next group, though the Trilobites differ specifically. 2. Menevian Group.-The list of fossils belonging to this group is now extended to more than forty species. Their distribution remains precisely the same as that elaborated in the last Report. The greater number of species occur with the largest Paradoxides, P. Davidis, which is the uppermost of the three forms known; P. Hicksii occurs at the base of the really dark shales, close upon the grey beds of the Harlech group just mentioned, in which group, 200 feet down, lies, as before noted, the P. Aurora. It is worth notice that these three species, with their accompanying smaller forms (Conocoryphe, Theca, Agnostus with each), keep close to their own particular domains, the species of Paradoxides being never found mixed together. This may serve to show how very perceptible a change of fauna may occur within moderate limits; for the section is perfectly continuous, and yet these Trilobites are confined to narrow bands and do not reappear. A species of Orthis, with few large plaits, has been found this year, the minute predecessor of all the Orthis tribe. Hitherto nothing but horny species of Brachiopods (Lingula and Discina) has been known to occur in these old beds; and one or other of these go down to the very base, while the Orthis is only found above the limit of the highest Paradoxides-beds. [The fossils exhibited gave a general idea of this old fauna; a much larger series is sent to the British Museum and Jermyn Street.] 3. With respect to the Ffestiniog group, or true Lingula-flag beds, we find this formation occupying its right place, at the very top of the Menevian group. It occurs in a faulted patch in Whitesand Bay; and forms a bold but narrow synclinal at the mouth of Solva Harbour and the Cradle Rock. It also occurs, of diminished thickness, in the district lying between the granite of Brawdy and Asheston and the syenitic axis. Upon it lies a trough of 4. Tremadoc Beds, or what we regard as such. They have only this year been worked out fully. And lying as they do upon the true Lingulaflag and under the Arenig or Skiddaw slate, they can hardly be anything but Tremadoc beds. They graduate by insensible degrees from the LingulaSandstones, first as bluish-grey slate, and then earthy grey thick-bedded rock of a peculiar tough texture, and contain the following fossils : Calymene, 2 species. Homalonotus, 1 species. - Asaphus, a giant species and a smaller one, the former all but undistinguishable from the Asaphus Homfrayi of the Tremadoc rocks. Orthoceras, with peculiar arched striæ. Nucula or Ctenodonta, 2 or 3 species. Orthis Carausii, a coarse-ribbed fossil, highly characteristic of these beds. Orthis, a fine-ribbed species like O. elegantula. Bellerophon, Lingula, Obolella. Now this fauna is wholly unlike the deep-water fauna of the Tremado c region. It is evidently a thin formation, deposited in much shallower water; and this may be the reason of the great change in the fauna. But there is something peculiar in the absence of the recognized upper beds of the Lingula-flags as they exist in North Wales. Instead of a recurrence of black slate for the Upper Lingula-flags and lower portion of the Tremadoc group (forming a very thick set of formations deposited in deep water), we have only a thin series of comparatively shallow water accumulations, marked by abundance of worm-tracks, and the fossils above quoted. This gives a marked character to the series, and indicates the following succession up to this point:- (1) Shallow-water or shore beds for the Harlech group. (2) Slow depression for the Menevian group. (3) Shallow-water or shore accumulations for the Lingula-flag. (4) Gentle depression for the Tremadoc. (5) And, lastly, deep and decided depression of the sea-bed to receive the next great formation-the Arènig Rocks (Lower Llandeilo, Murchison). 5. Arenig or Skiddaw Rock.—A formation at least a thousand feet thick, of vertical beds of black shale, seen in Whitesand Bay, and occupying also more than half of Ramsey Island, where they lie in a distinct trough of Tremadoc and Lingula-flags; and everywhere characterized by the following fossils :Eglina, 2 species. Ogygia, 2 large species. O. peltata and O. bullata. Asaphus, a large species. Trinucleus, 2 species. Ampyx, n. sp. Agnostus, Orthis, Lingula, Theca, Bellerophon. And, lastly, branched and twin Graptolites, viz. Dendrograpsus and Didymograpsus. No Graptolites occur beneath the Skiddaw group in Britain. And though all these species, except the Graptolites, are distinct from the fossils of the same strata in North Wales and Shropshire, the probable reason is, that the latter were in shallow water, while ours is evidently, like the Skiddaw slate, a deep-water series. We may therefore expect these species to be found in Cumberland. Ramsey Island is worth a visit; for the exhibition of the three sets of rocks (Lingula-flag, Tremadoc, and Arenig) is very complete on the north side of the island, and fossils are abundant. 6. To complete the geology of St. David's, one must go to the overlying Llandeilo flags of Abereiddy Bay. These fine slate-quarries are full of fossils. Trilobites of well-known forms, familiar to us at Builth and Llandeilo, crowd the slaty bands, and Graptolites in myriads, principally the species called the tuning-fork graptolite (Didym. Murchisona). The chief Trilobite is Ogygia Buchii; but there are many other Builth species, and some very rare ones, Barrandia Cordai, for instance. A few words on the faults of the district, which are literally innumerable. E. and W. faults, sometimes of large amount, but not much indicated on the surface. N.N.W. ones, more conspicuous as lines of valley and marsh; often shifting the strata much, and giving outline to the coast. N.E. faults, frequent, but not of very large amount; have not been well observed. N. and S. faults, believed to be the latest, and they give much impress to the features of the district, forming short valleys, and shifting the strata, but less than the others. Summary of the facts stated. 1. We have two axes of elevation in the promontory, viz. the granite of Brawdy and Asheston on the south-east, and the so-called St. David's syenite in the centre. The latter is chiefly altered rock. 2. Between these two axes, and on either side of them, the purple and grey Cambrian rock forms a steep trough, supporting black shales of the Menevian group, followed by Lingula-flag and Tremadoc rock, and on the north side of the coast Arenig or Skiddaw rocks covered by Llandeilo flag. 3. The conditions of deposit seem to be, that the Harlech group was nearly uniform with that of North Wales, but, being of finer grain, indicates a somewhat deeper-water deposit. The Menevian, Lingula-flag, and Tremadoc rocks are all much thinner, and, as a rule, of more even deposit, than in North Wales. They, too, seem to have been formed far out at sea, but probably in no great depth of water. The depression in the Arenig and Llandeilo groups seems to have been greater, and particularly in contrast with the conditions of deposit in North Wales and Shropshire, where shore accumulations were being everywhere laid down. But in this respect they are more like the Skiddaw slates, some of whose fossils they include; and the presence of repeated beds of lava, ash, and ashy slate lends no countenance to the idea that these beds were subject to the oscillations of a shallow sea; for the deposits are remarkably tranquil, fine-grained, and regular. Beds of fossils occur at intervals, only in the Arenig and Llandeilo rocks, and are then plentiful, as in other deep-sea deposits. But the Tremadoc rocks, being apparently laid down on a stationary sea-bed, present us with conditions wholly unlike those of the same period in North Wales, and, perhaps as a consequence of this, with a very different set of organic remains. The Harlech, Menevian, and Ffestiniog group have each large and well stratified beds of true contemporaneous volcanic rock, as well as many intruded beds. J. W. SALTER. Report on Dredging among the Hebrides. THIS exploration lasted nearly two months, viz. from the 24th of May to the 14th of July in the present year. It comprised Sleat Sound, Lochs Alsh, Duich, Slapin, and Scavaig, and the Minch from Croulin Island to Loch Ewe. I had a good cutter yacht, the master of which had been employed by me for many years as dredger and took considerable interest in the work, an active and willing crew, four serviceable dredges, 300 fathoms of new rope, machinery for hauling up the dredges, a large tub, sieves, and various other apparatus. The Hydrographer of the Navy obligingly supplied me with such charts as I required, to show the depths and nature of the sea-bottom in the district which I proposed to examine; and these were of great use in dredging, as well as for navigation. The weather was too fine; we were often becalmed for many hours together: and instead of steady breezes, we had too many of those squalls which are so prevalent, and occasionally dangerous, in the Hebrides. The Hebridean seas have been often searched, but not explored, by zoologists. Their great extent, and the number of lochs and inlets which indent the coast in every direction, would render necessary an immense deal of money, time, and patience for a complete investigation. There is little probability that the subject of the present Report will ever be exhausted. The Invertebrate fauna of this district is of a northern character, although there are a few exceptions. Such are, among the Mollusca, Trochus umbilicatus, Phasianella pulla, Rissoa cancellata or crenulata, Odostomia lactea or Chemnitzia elegantissima, and Pleurobranchus plumula. These may be regarded as southern forms. The first and third occur as far north as Stornoway; the second ranges to Dunnet Bay in Caithness; of the fourth I dredged a single specimen in the upper part of the Minch; and the last lives between tide-marks in the Isle of Mull. As a set-off to the above, I would mention the following species, which have now for the first time been found so far south as the Hebrides, viz. Montacuta tumidula (a new species, which I will presently describe), Trochus occidentalis, var. pura, Jeffreysia globularis, and Odostomia eximia. The first is Swedish; the second is Zetlandic, Scandinavian, and North American, although it has also been procured in the Orkneys and on the Aberdeenshire coast; the third is Zetlandic, and the fourth Zetlandic also and Norwegian. It must be borne in mind, as regards the extent of geographical distribution, that the southern extremity of the Shetland Isles is distant about 200 miles from the northern extremity of the Hebrides, as the fish swims." Besides the four last-named species, the following seem to reach their most southern limit in the Hebrides :-Lima elliptica, Leda pygmæa, and Trochus Grænlandicus. Leda pygmaea has 66 indeed been dredged on the coast of Antrim; but I am now inclined to regard the specimens thus obtained as quaternary fossils. Tethea cranium (a sponge not before known south of Shetland) occurred in tolerable numbers on the Ross-shire side of the Minch. Species of Mollusca, inhabiting the Hebridean seas, which are in the main northern (although they have been found somewhat further south, and some of them occasionally even in the Mediterranean), are-Argiope cistellula, Pecten striatus, Mytilus phaseolinus, Modiolaria nigra, Crenella decussata, Nucula tenuis, Leda minuta, Arca pectunculoides, Montacuta ferruginosa, Cyamium minutum, Cardium minimum, Cyprina Islandica, Astarte compressa, Tellina pusilla, Scrobicularia nitida, Thracia convexa, Mya arenaria, M. truncata, Chiton Hanleyi, C. albus, C. ruber, C. marmoreus, Tectura testudinalis, T. fulva, Propilidium ancyloides, Puncturella Noachina, Emarginula crassa, Scissurella crispata, Trochus helicinus, Lacuna divaricata, L. puteolus, L. pallidula, Rissoa albella, Jeffreysia diaphana, J. opalina, Odostomia minima, O. albella, O. insculpta, O. diaphana, Velutina plicatilis, V. lævigata, Trichotropis borealis, Purpura lapillus, Buccinum undatum, Trophon Barvicensis, T. truncatus or Banffius, Fusus antiquus, F. gracilis, Nassa incrassata, Mangelia turricula, Defrancia scabra, Cylichna nitidula, Amphisphyra hyalina, Philine scabra, P. pruinosa, and P. quadrata. For certain species, which are almost peculiar to the Hebrides, I am not aware that any locality has been recorded between that district and the Mediterranean. Such are Axinus ferruginosus, Poromya granulata, Neœra abbreviata, N. costellata, and Cylichna acuminata. The first three of these were described by the late Professor Edward Forbes, in the Report to the Association in 1843 on Egean Invertebrata. Another Hebridean species (Nucula sulcata) is not found southwards nearer than the coast of Spain. Some of our most conspicuous and prized shells, that are also of a northern type, are wanting in the Hebrides. Saxicava Norvegica, Natica Grænlandica, Buccinum Humphreysianum, Buccinopsis Dalei, Fusus Norvegicus, F. Turtoni, and F. Berniciensis, are in this category. All the above (with the exception of Buccinum Humphreysianum, which inhabits Shetland and the coasts of county Cork) are met with on the Dogger bank; and the first two are fossil in the Clyde beds. Six out of the seven being univalves, I would venture to surmise that their non-existence in the western seas of Scotland may have arisen from the circumstance that the diffusion of uni |