treble rows peculiar to the shark; but the animal must have been of a small species, or more probably a young one. The tooth g is figured from Agassiz, (Carcharias Megalotis,) and figure h, from a drawing by Dr Mantel, of the squalus mustelus, in the Wealden beds of Sussex. At Woodhall, on the north side of the Pentland Hills, the coal strata are exposed on the banks of the Water of Leith. In a stratum of shale, lying below ten feet of sandstone, an immense number of the bivalve shell, plate 2, figs. a and b, are visible. The only figures of shells in the least resembling these, which I have seen, are in Cuvier and Brongniart's Illustrations of the Paris Basin, (Ossmen. Fossil. tom. ii.) supposed Cytherea convexa; and in vol. iv. pl. 314. of Sowerby's Fossil Conchology, under the name of Axinus obscurus, said to be found in magnesian limestone. Both species differ from the figure here given, which may be named, from its locality, Axinus Pentlandicus.

Figures c, d, e, f, are unios from the coal shale at Polmont, near Falkirk; c appears almost identical with Sowerby and Mantel's Unio antiquus of the Wealden. Figure d is the same shell shewing the hinge.

Fig. f. resembles the Unio compressus of the same locality.

Figures h h are minute shells, found in great numbers in the Burdiehouse limestone, supposed to be of the genus Cypris. Species of these are abundant in the Sussex beds.

Figure g is evidently a modiola, found in the same beds with Axinus Pentlandicus, at Woodhall, and differs little from the existing species.

Sphenopteres and equisite are also abundant in this shale. The Sphenopteris affinis found in Burdiehouse seems analogous to the S. Sillimanni of the Wealden beds, figured in Dr Mantel's work.

The above list contains the whole genera of fossil animals yet discovered; and the number of species may amount to about seventy. It will be observed, that the greater proportion of species belong to the order Pachydermata, or thick-skinned animals, and consist chiefly of those that are aquatic, or that frequent the banks of rivers. Now, when we consider the nature of the strata of which our present continents are formed, consisting almost exclusively of marine and fluviatile deposits, this is just the sort of terrestrial animals that we might expect to find enveloped in these strata.

In this list, species of the Hippopotamus, horse, beaver, weasel, hare, dog, fox, ox, deer, camel, have been found so nearly resembling living species, as to warrant their being pronounced identical, while others differ only in a slight degree from existing species.

The geographical localities of these fossil remains are here given, which point out a distribution in many cases different from that which prevails at present.

NOTE VI. p. 59.

FORMER TEMPERATURE OF THE EARTH.

After alluding to the theories of central heat and increased volcanic action in former ages, Sir J. Herschel observes, "Neither of these can be regarded as real causes in the sense here intended; for we do not know that the globe has so cooled from fusion, nor are we sure that such supposed superior activity of former than of present volcanoes really did exist. A cause possessing the essential requisites of a vera causa has, however, been brought forward by Mr Lyell, in the varying influence of the distribution of land and sea over the surface of the globe; a change of such distribution in the lapse of ages, by the degradation of the old continents and the elevation of new, being a demonstrated fact, and the

influence of such a change on the climates of particular regions, if not of the whole globe, being a perfectly fair conclusion, from what we know of continental, insular, and oceanic climates, by actual observation. Here, then, we have a cause, at least, on which a philosopher may consent to reason: though whether the changes actually going on are such as to warrant the whole extent of the conclusion, or are even taking place in the right direction, may be considered as undecided till the matter has been more thoroughly examined."-Discourse on the Study of Natural Philosophy.

The distribution of heat on the surface of the globe, and the modifications of climate as influenced by the excess or deficiency of land, is a subject full of interest, and has been beautifully illustrated by Humboldt, in his remarks on Isothermal lines. (For a summary of his treatise see Edinburgh Philosophical Journal, vol. iii. 1820.) Without a knowledge of this subject, the true import of Mr Lyell's theory of change of temperature cannot be sufficiently appreciated.

NOTE VII. p. 61.

Those geologists who believe in the existence of a previous world reckon all the strata below the superficial diluvium as belonging to this ancient state of things, and that the creation of the present earth and present system of things commences with the soil and vegetation above this diluvium, the effects of the deluge being supposed to have been of a slight and transient nature, and to have left no proofs behind. Professors Buckland and Sedgewick, the Rev. Mr Conybeare, and many others, avow this opinion.

Cuvier believed the present system of things to have commenced immediately after the deluge, when the present surface was elevated above the level of the ocean.

A third party ascribe no definite period to the com

mencement of the present system, but allow that man was introduced upon the earth at the period indicated by historical record. Hutton, Playfair, and Lyell, adopt this opinion.

NOTE VIII. p. 64.

The effect of rivers wearing down their channels we have remarked in several of the waterfalls in Scotland, particularly at the Cauldron Linn, or waterfall on the Devon, in Clackmannanshire, where there is a sinking of the fall of ten feet through a chasm worn in the hard greenstone rocks. The gradual progressing of the fall of the mighty Niagara upwards to its source in lake Erie, is also well exhibited in the frontispiece to Bakewell's Elements of Geology, 4th edition. From this sketch it appears that the river Niagara, which flows out of lake Erie, has, in the course of ages formed a deep channel, of seven miles in length, from the present falls to Queenstoun, and that the cataract has, in all probability, been situated at this lower point when it first began to flow, but that it is now progressively wearing upwards. Mr Fairholm has also some interesting calculations on the probable time which has been necessary for the river to excavate this course.

NOTE IX. p. 75.

FABER'S EXPLANATION OF THE MOSAIC DAYS.

"The divine Sabbath, instead of being limited to a single natural day, is, in truth, a period commensurate with the duration of the created universe. What that duration will be, no one knows, save the Father only, (Mat. xxiv. 36;) but this we know, that according to the