Jura. These two together constitute a great part of the chain of the Jura Mountains, which extends from Geneva to Schaffhausen, and is also prolonged into Suabia. In the northern chain of the Jura from Schaffhausen to Geneva we meet with numerous places where the rocks are filled with fossils, which teach us both by their number and their nature that the depth of the ancient sea there could not have been considerable. By comparing, for instance, the most important animal remains found fossil in the beds at Porrentruy with the habitats of species actually living in the different oceanic zones, we can mark off proportionately corresponding depths in both, and thus correlate the old Jurassic deposits with the existing deep waters. Thus, at about one hundred feet of depth now live, and must have formerly lived, 15 species of the shells named Trochus and Turbo; 6 of the Pleurotomaria, 13 of the Pterocera, 6 of the Melania, 32 of the Cardita; so on in succession. At depths of from 100 to 600 feet now live, and must have formerly lived, the Pecten, Cardium, Modiola, Arca, and a species of Cidaris, while in the very deep zones from 600 feet downwards, live, and must have primevally lived, Arca, Pecten, Cidaris, and certain tiny many-chambered microscopic shells. Such is an example of the safe application of a scale noted by the habitats of living to the rock-registered dead, and in this manner we approximate to the depths of the Jurassic waters of the old world. In the White Jura of Porrentruy we can distinguish twenty-seven beds, each one of which is characterised. by its particular petrifactions, or by the absence of some, and by the presence of others. It is estimated that twenty varied fauna lived in these spots successively, subject to the same modifications which govern our present seas and continents, but with such slowness as to demand an incalculable number of ages for the now apparent rocky result.

If now we regard the Brown Jura, which is composed in great part of compact limestone marked by granules of oxide. of iron, we can follow it along the Alps from Gonzen, in the canton of St. Gall, across the cantons of Glarus, Uri, and Unterwalden as far as the chain of the Stockhorn and the environs of Leuk. This great mass is subdivided into the superior, the middle, and the inferior stages, each of these likewise being characterised for the most part by particular fossils. If we would therefore obtain a total vertical depth of the Jurassic Sea, we must begin from the surface with the White Jura, which we may take as 817 Swiss feet, and add for the Brown Jura about 900 feet, giving for the White and the Brown 1,700 feet together. The Black Jura, if we include

the liassic series under the general term Jurassic, would require a further 300 feet; and thus the thickness of the combined aggregate would certainly amount to 2,000 feet.

Most numerous were the molluscs in this great sea, presenting a marvellous variety of forms in such prodigious abundance that they performed a principal part in the formation of the subsequent rocks, and specially characterised some Jurassic stages. The genus Nautilus was represented by thirteen species, of which one (Nautilus giganteus) acquired huge dimensions. The well-known Ammonites were equally abundant and equally large or sometimes even larger, being comparable to cart-wheels. We have nearly all the species in our English oolites, and several of them are found in the same strata throughout Europe. Then there were the dart-like Belemnites, near neighbours to the Ammonites, and occupying a great area in the same sea. Of these the museum at Zurich possesses sixty-six species from the Swiss lias and jura, mostly the upper lias, the brown and the lower white jura beds. The cephalopods were indeed the principal and the most abundant univalves in the Jurassic ocean; but they were accompanied by other and very numerous genera. Amongst those which still frequent the seas and rivers of our hot zones we find at Porrentruy the genera Melania, Chemnitzia, and Neritinæ. In the ancient sea we are now regarding, the Bivalves were in number nearly double the Univalves, although presenting but a small variety of forms. Shells and shell-inhabitants of many kinds there were in these waters, and their fossil remains testify to their abundance, to their similarity in many instances to still living genera and species, and to their extinction in the case of others.

In the Swiss Jurassic ocean the fishes were very few, constituting about a dozen species; and of the greater part of these the teeth only are met with in these rocks. If we include the lias in the term Jurassic, it may be remarked that fish were at this period numerous in England. Fine examples of Ganoid fishes have been found in the lias of Lyme Regis and elsewhere on the Dorsetshire coast, and are stored in our public museums and private cabinets. Marine plants flourished, no doubt, luxuriantly on the rocks of the Jurassic ocean, but their soft nature and surrounding conditions were unfavourable to their preservation and petrifaction. Hence it is impossible to determine from their indistinct remnants more than a few important forms. They were of the nature of spreading sea-weeds, scientifically named Fucoids, Nulliporites, Chondrites, and Cylindrites.

VOL. CXXXIX. NO. CCLXXXIII.

M

During this long marine epoch there were several islands which presented a terrestrial fauna and flora in close vicinity to the great seas. In Switzerland we can, as elsewhere, by their fossil remnants distinguish the sites of these ancient islands. Some have been traced in the canton of Bâle, others in the environs of Olten and of Mount Rissoux in the Val de Joux. Diligent study of fossils enables us to repeople these sites of islands with their once living tenantry, and to show them as they then appeared, though never to the eye of man. At least four species of plants grew upon them; one a conifer, another a fern, the third a Zamites, and a fourth a Cycadopteris, a genus of ferns peculiar to the Jura. These were terrestrial plants suitable to the soil of a tropical island, and we can add to them from our contemporaneous deposits of Yorkshire and the Isle of Portland. In the latter there lies a remarkable deposit of the remains of a similar flora, wherein numerous Cycads exhibit forms analogous to the Zamites of South Africa. What the quarrymen in the Isle of Portland call Birds' nests' are in fact fossilised Cycads capable of being sectioned and polished, and then showing their true botanical interior structure. In all probability our Isle of Portland was a Jurassic isle like those in Switzerland which we are now describing. The borders of these ancient islands were adorned then with Cycads having magnificent pinnated leaves, with tall Araucaria and Arthrotaxites, under the shade of which strongly-mailed crocodiles pursued their prey. As in like islands of our time, there were also on the beaches numberless tortoises and turtles, which came to deposit their eggs in the sands. The submarine rocks were covered, then as now, with growing forests of coral, in which were labouring millions upon millions of constructive insects, while in the darker crevices of these stony thickets were hiding innumerable molluscs of richest colouring. Marine sponges, star-fish, and urchins were not absent or infrequent in these haunts of old life.

In various species of coral-forming polyps the Jurassic sea was remarkably rich, the White Jura at Porrentruy alone containing more than 107 species. In the madrepore isles of that time there lived a variety of forms which may be ranged under three principal classes: 1st. large Polypiers in the shape of a dome; 2nd. others which were shrubby and branching; and 3rd. those which assumed a cup-like form. Amongst these were sponges of diversified shapes, carpeting the seabottom with beautiful colours varying from sombre blue to sulphureous yellow; as they do in the oceans now rolling. Next to these came numerous sea-urchins (or Echinidæ,)

which so flourished in the old Jurassic waters, that seventy-five species of them have been distinguished in the White Jura of Porrentruy, to which might be added a great number of others from more ancient stages. The beautiful genus Cidaris, which is capable of living at great depths in known oceans, was largely represented in the Jura; and there its tests and spines are frequently found in the rocks.

Upon the Cretaceous epoch in Switzerland we can only bestow a passing glance. It duly there, as elsewhere, succeeded the Jurassic, but the Chalk proper, the main constituent of the Cretaceous epoch, is wanting in Switzerland. There the rock masses representing it consist principally of a compact calcareous rock, very different from the familiar English chalk. One or two facts connected with the Sewerkalk, so called from the calcareous rocks occurring at Sewen, near Gersau on the lake of Lucerne, will interest us. Microscopically viewed and magnified fifty times, it is seen to be full of minute Polythalamous shells. The work and results of these tiny creatures belong rather to the department of study now styled Microgeology than to the general descriptive science. They are, however, deserving of a passing notice from the minuteness of their form and the magnitude of their labours. Although we cannot see them with the unaided eye, nor even find them with a common lens, yet if we take a piece of the stone and polish and oil it, and then place it under the microscope we discern fine lines which represent the walls as it were of their chambers. A special preparation is essential to the distinguishing of these fine lines in sufficient numbers; and few persons would persist so patiently as Professor Kaufman of Lucerne in attempting to make these extremely faint lines of division visible to the observer. These inconceivably tiny creatures have from the invisible built up the visible, and literally out of less than molehills have made mountains. The cretaceous rocks in the calcareous mountains around the lake of Lucerne are due to them, and what is now hastily taken in by a passing glance of the eye of an inconsiderate tourist, has cost billions upon billions of these microscopic architects thousands of years to pile up in the long past ages. Of the English chalk much the same may be said, since its builders and their work were similar.

Continuing our stratigraphic ascent we reach another geological epoch, the Eocene, the time of the dawn of Tertiary life; and we shall now treat of some formations distinctive of Switzerland. One of these is the fossiliferous slate of the canton of Glarus, and some other localities. On arriving

at Wesen by the railway which connects Zurich with Coire we observe a narrow valley which is flanked, within a limited area, by a grand mountainous mass. The base of this valley is verdant, covered with cultivated fields, or with grass prairies, and animated by large and populous villages. The inhabitants claim our sympathy by the manifest results of their laborious pains in creating a scene so industrial and cheerful out of so few natural resources in the midst of barren though imposing mountains. At Schwanden, the principal valley branches out into two secondary long Alpine valleys; one of these, which runs eastward, is named the Sernfthal, from its little stream the Sernf, and the other running westward is the Linthal, similarly named from its river the Linth, the village of Linthal being situated in a picturesque region covered with fields and prairies. Huge calcareous mountains form the sides, and rocks the bottom of the Linthal. To most British mountaineers the middle Glärnisch, the Bachistock, the Selbsanft, and the famous Tödithe Mont Blanc of the district-are familiar. Even invalids who frequent the baths of Stachelberg can see something of these mighty masses from the grounds of the Baths; but strong-limbed pedestrians may all along this grand valley make most delightful excursions.

We are not now, however, mountaineering but geologising; and must inspect the constitution and contents of some of these rocks. Let us direct our course towards the little village of Engi, near which are the quarries affording the slate-beds of this region, and from whence slates are exported afar, as well as employed near at hand. At a place called Matt, we already hear the noise of hammers heavily and hardly at work upon the slate-blocks of the heights above. Upon a nearer approach to those heights, and at 2,970 feet above the sea-level, we observe workmen labouring at thirty or forty different points in detaching the blocks, while others are waiting to transport them to the slate-cleaver. This scene on a small scale recalls to our minds the far more productive and imposing Penrhyn and Llanberis slate-quarries in North Wales. Geologically, however, the Swiss slates are much more interesting than the Welsh, since the Swiss slate mountain is as renowned amongst naturalists for its petrifactions as amongst slate-merchants for its slates, which cover Swiss houses beyond number, and even find their way into the village schools.

The primeval sea under which this deposit was formed was probably very deep, for on this supposition alone can we account for the absence of molluscs and sea-urchins. The bottom was composed of a pulpy or sandy slime, quite unfavourable to the