Our knowledge of the limits of animal life have been notably extended during the year which has just departed. Air, blown upon an adhesive surface by the aeroscope on the summit of Etna, twelve thousand feet above the sea level, has been found to contain large quantities of Diatomaceæ; and thus the presence of a zone of life has been discovered to us, soaring not only above the limits hitherto fixed, but above the range of physical phenomena in the mountain itself.

And now the ocean-depths have given up a secret as marvellous. We are taught that at a depth below the surface nearly as great as the height of the infusorial zone above it, animals as high in the scale of being as starfishes are enjoying life. The one discovery is a fitting pendant to the other, and yet, how great is their difference! In the one case the extreme ratification of the atmosphere seemed to our notions to render life impossible; in the other, the enormous pressure of the opposite element, which in the homes of these starfishes must amount to at least a ton and a-half on the square inch, is so greatly at variance with our belief, that we are confounded at the very outset of the inquiry. The capability in an animal so well accustomed to air as the starfish—whose ordinary domain is the seabeach—to exist without it, and its inherent power of withstanding a pressure that would upon the surface grind a rock to powder, are studies replete with instruction and value—studies which can be turned to a good geologieal account, and made to bear reference to a past fauna as well as to a living one.

Not a great many years ago the “bigwigs” in England were assembled in conclave, and the élite of science was called before them. There were a great many lumps of a blackish-brown substance on the table, and a great deal of smelling, and burning, and poking of the same black lumps by the same “bigwigs” and learned men. It was the great “Torbane Hill Coal” case.

“The point was in question, as all the world knows, To what the said substances ought to belong.”

Was it pure carbon? Was it carbonaceous shale? Was it shale without much carbon? Was it carbon without much shale? Was it bituminous shale? Was it coal-shale? Was it cannel? Was it coal?

We are afraid to say how many guineas were spent, or how many microscopes were busy in London and Edinburgh. But after all the question was simply this, “What is coal?” We are not going to try to give a definition; but if we can show our young readers (and there are, we hope, a good many of them) a few of the facts connected with the structure, contents, mode of formation, &c., of a coal-field, perhaps we may be able to answer the formidable query, “What is coal?” without calling in the aid of counsel, and our fee is—one shilling. As this is a Christmas lecture for our young friends, we hope our senior readers will not take it amiss if elementary phrases are introduced, and a few woodcuts given to illustrate what they know very well. And perhaps we may be allowed to speak in the first person singular; it is more conversational.

When a mineral presents itself under a form which does not belong to it, there is then what I shall call pseudomorphism.

The substance from which the mineral borrows its form may be of any kind—inorganic or even organic. It is called original or pseudomorphosed, while the mineral which replaces it is called pseudomorphic.

Pseudomorphism by alteration is that in which the pseudomorphic mineral still contains the elements of the original substance. Pseudomorphism by displacement is that in which this is not the case. In order to understand the difference which exists between these two kinds of pseudomorphisms, it suffices to mention as examples ironpyrites, which changes into limonite, still preserving its crystalline form; or fluor, which after being completely destroyed, is replaced by quartz. The name of paramorphism has been given to the kind of pseudomorphism which is produced without modification of chemical composition. Arragonite changed into calcite, and pyrite changed into marcasite are examples.

At first sight it seems that these metamorphoses of minerals must be very exceptional, but observation teaches us, on the contrary, that they are met with in a number of localities; they are, moreover, extremely varied. In fact, they include all the alterations to which minerals are subject in their structure and in their chemical composition. They include also, as a particular case, the decomposition of minerals; and kaolin, for example, results from a true pseudomorphism of felspar.

Amiens and Abbeville do not, however, enjoy a monopoly in these flint implements; they are found, apparently, all over the earth. At any rate, we can boast in our land of such treasures, and we can proudly record that the first discovered specimens belong to England. Let Amiens and Abbeville by all means be commemorated as the scenes of M. Boucher de Perthes' persevering investigations, which have furnished the incitement to the present remarkable inquiry—let the names of Boucher de Perthes, Prestwich, Falconer, Flower, and Evans, be duly honoured as the pioneers of the investigation; but let us also think of Hoxne, Grays, Ilford, Maidstone, Stanway, and the scores of other places where mammalian bones have been found in our own land—and, let us hope that our young geologists will set to work, and reap a rich harvest in the yet ungarnered fields. Does not this first recorded implement—this earliest discovered relic—(fig. 5) treasured and preserved in the Sloane collection, the nucleus of the British Museum, and entered in that old catalogue, two hundred years ago—encourage them. Does it not say in unmistakable language “Under your feet these relies may be found?”

There is another of these spear-shaped flints, which has obtained a great deal of notoriety in the late discussions. It was found at Hoxne, in Suffolk—a place memorable in the history of the good king Edmund, the saint and martyr—and was described, and figured in the “Archæologia,” (see cut 9, p. 20), by Mr. Frere, the finder, who, with remarkable acuteness, seems to have fully comprehended the value and true bearing of his discovery. His paper is, even now, an excellent epitome of the subject; and we give it at length, just as it was read in 1797, before the Society of Antiquaries of London.