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bare by sweeping them away. Let us but imagine that this disturbing rock began to rise under the earlier impulsions of the elevating agencies, and during the deposition of some one of the later secondary formations, as the precursor of the granitic range,—that the superincumbent Lias, already existing in its present consolidated state, opened into yawning rents and fissures over it, as the earth opened in Calabria during the great earthquake,—and that the loose sand and calcareous matter which formed the sea-bottom at the time, borne downwards by the rushing water, suddenly filled up these rents, ere the yielding matrix had time to lose any of its steepness of side or sharpness of edge, which it could not have failed to have done had the process been a slow one. The sandstone dikes, apparently Oolitic, mark, it is probable, the first operations of those upheaving agencies to which we owe the elevation of the granitic wall, and which, ere they accomplished their work, may have been active during occasional intervals for a series of ages. I am not of opinion that the accompanying marks of alteration among the shales and limestones of the beds are sufficiently unequivocal to render imperative some more fiery theory.

CONTEMPORARY AND EXTINCT TYPES OF THE LIFE OF THE TEREBRATULA.

We find among the earliest bivalves of the Silurian system the delicate Terebratula, with its punctured umbone; we follow it downwards through all the various formations, and see it appearing on each succeeding stage, specifically new, but generally old, until, quitting the rocks with their dead remains, we pass to the existing testacea of our seas, and find among them the ancient Terebratula still extant as a living shell. Contemporary as a genus with every extinct form of animal life, we find it contemporary with the last of created beings also,—contemporary with ourselves; and the Terebratula is but one existence of a class to which, though their generic antiquity may be rather less remote, nearly the same remark applies. The ostrea still exists,—its congener and contemporary the gryphaea has perished; the nautilus survives,—its congener and contemporary the ammonite is long since dead; the cuttle-fish abounds on our shores,—its congener and contemporary the belemnite is to be found in only our rocks. And thus the list runs on. We can scarce glance over a group of fossils, whatever its age, which we do not find divisible into two classes of types,—the types which still remain, and the types which have disappeared. But why the one set of forms should have been so repeatedly called into being, and why the other set should have been suffered to become obsolete, we cannot so much as surmise. Why, it may be asked, should the nautilus continue to exist, and yet the ammonite have ceased with the ocean that deposited the Chalk 1 or why should we have cuttle-fish in such abundance, and yet no belemnites t or why should not the gryphaea have been reproduced in every succeeding period with the oyster? In visiting some old family library, that has received no accessions to its catalogue for perhaps more than a century, one is interested in marking its more vivacious classes of works,—its Spectators, and Robinson Crusoes, and Shakespeares, and Pilgrim's Progresses, in their first, or at least earlier editions, ranged side by side with obsolete, longforgotten volumes, their contemporaries, that died on their first appearance, and with whose unfamiliar titles one cannot connect a single association. But it is always easy to say why, in the race of editions, the one class should have been arrested at the very starting-post, and why the other should have gone down to be contemporary with every after production of authorship, until the cultivation of letters shall have ceased. It is otherwise, however, with the geologist. He finds he has exactly the same sort of fact to deal with, —an immense multiplication of editions, in the case of some particular type of fish, or plant, or shell, and in the case of other types, no after instances of republication; but he finds himself wholly unable to lay hold of any critical canon through which to determine why the one class of types should have been so often republished, or the other so peremptorily suppressed. And yet, were all the circumstances known, it is possible that some such canon might be found to exist . Geology is still in its infancy. Shall a day ever arrive when, in a state of full maturity, it will be able to appeal to its fixed canons, and to say why one certain type of existence was fitted for but one definite stage in the progress of things, and some other certain type fitted, by a peculiar catholicity of adaptation, for every succeeding period 1

SIR DAVID BREWSTER ON THE CUTTLE-FISH AND BELEMNITE.

The following discovery of Sir David Brewster, regarding a marked peculiarity of structure in the eye of the cuttlefish, now first made public, will be deemed of great interest by all who have learned to admire that inconceivable variety of design in the works of the Infinite Mind which grows upon the inquirer the more he examines, and which, if man were not immortal, it would be an error of his very nature to have the strong existing desire to examine :—

St. Leonard's College, St. Andrews.

My Dear Sir,—I have been reading, with great pleasure, your interesting account of the cuttle-fish, and was glad to find that you had noticed the singular structure of its eye. During the last twenty years I have dissected literally hundreds of cuttle-fish eyes, but I never published my observations on them, in consequence of having found singular discrepancies in the eyes of different species, and having been always expecting from America the eyes of the remarkable varieties which occur there, and which have been repeatedly promised me by American naturalists.

As you will take a great interest in the subject, I shall endeavour to give you some idea of what I have done.

Independent of the peculiarity which you have noticed, of there being no aqueous chamber between the cornea and the lens, there is no iris and no pupil, the quantity of light admitted being regulated by the eyelids.

The lens itself is of a most singular description. It consists of two lenses sticking together, and capable of being separated without injuring either. This structure is unique.

The lens D A E C consists of two, D A

a" K* V. E, and a meniscus, m C «, which is kept B V J 1 cse to D A C by a double cartilaginous J j J ring, D E. The dimensions are D E = _\£ U 0*51 inch, A C = 0*433 inch, A B = EF o'3433 inch, B C = 0*09 inch; m n =

0"333 inch. The outer diameter of the front ring, D F, is = o"59 inch, and its inner diameter = 0*31 inch.

In some indurated lenses I find the lens C to be doubly convex, and the surface of the lines D E A, on which it rests, concave. This must have been the lens of a different species.

The fibrous structure of the lens is very remarkable. The laminae, or coats, of the lens are parallel to D A E and m C n; and the fibres of the lens DAE diverge from A as a pole, like the meridians of a globe; and they all terminate, not in another pole, but in the surface D E, or that which corresponds with m 0 n. This termination of the whole component fibres of the lens D A E in a surface is quite unique, and the mode of converting this rough plane (like a shaving-brush cut across), into a smooth surface, is singularly beautiful. Each elementary coat, or lamina, being composed of fibres, has at its termination in the periphery D E a sort of selvage, where all the fibres end; and these selvages, being circles, fill up, as it were, or compose the flat surface of the lens.

The coats, or laminae, consist of fibres different from those of all other animals. When other lenses harden, they form a solid body, transparent like a gum; but the cuttle-fish retains its laminated structure, and shines with all the brilliancy of a pearl.

In the Scepia Electona the front lens A separates from B in the line m a b c n, a peculiarity which I have never found in the Scepia Loligo. The diameter A B is larger than m n.

It would be curious to find the lenses in a fossil state.

I have found some lenses of the Scepia Loligo of a paraboloidal form. It is probable that the form of the lens varies with the age of the animal.

When the lenses become indurated, they often exhibit the most beautiful internal reflections, and I have often thought of having them set as brooches. The pearly structure is produced by long exposure under ground; and it is almost impossible to distinguish such lenses from pearls when the convex part only is shown.—I am, my dear Sir, ever most truly yours,

D. Brewster.

To Hugh Miller,

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