Beach Rambles in Search of Seaside Pebbles and Crystals / With Some Observations on the Origin of the Diamond and Other Precious Stones

by John George Francis

As to our seaside pebbles, the most compact of them are even visibly porous. Cut through the hardest jasper, and polish one face till it shines like a steel mirror, and then hold it so as to reflect the light, you will at once discern numerous minute specks or flaws on this surface, as if the point of a needle or graving-tool had been busily at work upon it. These specks have always been there. They are air-holes, and in the case of a fossil-pebble were, some of them, doubtless, connected with the position which the animal occupied just before he died. These air-holes must have traversed this hard stone in every direction, for, cut the pebble how you will, you meet with them. Others again, incomparably more numerous, but which can scarcely be discerned without the aid of a powerful microscope, are the true pores belonging to this apparently impenetrable substance.

I have found that the action of daylight tells even upon polished agates after a time. Some of the spots and markings in the finest stones grow fainter in the course of many years. Others appear to deepen. This is, no doubt, a change resulting from the oxygen, contained in a beam of light, acting readily upon carbon, silex, and other substances. And it furnishes an independent argument for concluding that the visible beauty of these formations, in perpetuating a coloured pattern, has been due rather to mixed chemical processes than to pure crystallography.

The fossil nodules, mostly siliceous, which we find upon a sea-beach, are integral specimens. It never but once happened to me to meet with what appeared to be two choanites in the same pebble, and I incline now to believe that this was in fact one choanite who had divided himself after the manner of the Luidia. But even supposing that here were, indeed, a pair of perfect animals, when it is considered that this was one single instance, occurring among more than a thousand picked up by me, in which the choanites were always solitary, such an exception may be almost said to prove the rule.

The late lamented Hugh Miller has stated the like fact concerning his Morayshire and Cromarty icthyolites. At pp. 194, 195, of his “Cruise of the Betsy,” he remarks that “the limestone nodules take very generally the form of the fish which they inclose; they are stone coffins carefully moulded to express the outline of the corpses lying within.” Then, after observing that the shape of the stone conforms to the attitude of the fish in every instance, he goes on to state that “the size of the fish regulates that of the nodule. The coffin is generally as good a fit in size as in form; and the bulk of the nodule bears almost always a definite proportion to the amount of animal round which it had formed.”

He then gives, in his usual clear and graphic language, the following remarkable statement, the result of direct experiment.

“When a calcareous earth, mixed up with sand, clay, and other extraneous matters, was deposited on some of the commoner molluscs of our shores, it was universally found that the mass, incoherent everywhere else, had acquired a solidity wherever it had been penetrated by the animal matter of the molluscs. Each animal, in proportion to its size, was found to retain, as in the fossiliferous spindles of the Old Red Sandstone, its coherent nodule around it. Here the animal matter gave solidity to the lime in contact with it. But in the natural phenomenon of the icthyolite beds, there was yet a further point, for in these the animal matter must have possessed such an affinity for the mineral, as to form, in an argillaceous compound, a centre of attraction powerful enough to draw together the lime diffused throughout the mass.”

Hugh Miller concludes the above passage by saying that “it still remains for the geologic chemist to discover on what principle masses of animal matter should form the attracting nuclei of limestone nodules.”

Upon which last remark, I would suggest that the principle of the “law of definite proportions,” established by Dalton, and fully borne out by all succeeding experiments in chemistry, appears to meet the case, geologically as well as chemically, in every respect. For such a law must of course obtain, whether the chemical ingredients be present in the forms of mineral, vegetable, or animal life; in fact, we have never known the law to vary. It holds for the compounded elements which we term AIR and WATER; it holds for the crystals; it holds for vascular and cellular tissues; why should it fail when the further instance of a mollusc or a zoophyte is in question?

I see no reason to doubt that the blood, muscle, membrane, or adipose matter of any animal have their due respective affinities for the different substances of the mineral creation.