In a paper read before the Geological Society on the 23rd of April, 1856, I referred to the proofs of a “plasticity,” or imperfect liquidity, in the crystalline igneous rocks at the time of their protrusion, and called attention to the mechanical changes, in texture and structure, which could not fail to have resulted from the mutual friction of the component crystals or granular particles of these rocks, during changes of volume or of position, occasioned by variations in their temperature while subjected to intense and irregular pressures.

In illustration, I referred to the “ribboned” pitchstones and trachytic lavas of Ponza, Ischia, Hungary, Mexico, &c., in which this structure had unquestionably been produced in that manner, and I repeated the opinion (to which more than thirty years back I had given expression), that to such internal friction of the component crystals, was probably owing the foliation of gneiss and mica-schist; through the “squeeze and jam” to which the lateral portions of an eruptive granitic axis must have been subjected, between its own expansive force and the resistance and pressure of the overlying strata.

The subject has so important a bearing on Geological Dynamics and the doctrine of Metamorphism, that I trust to be excused for carrying the inquiry a little further. In doing so it will bo well to begin by some elementary considerations.

It is the well-known property of most substances to pass from a solid to a liquid state, and vico versâ, under varying circumstances of temperature and pressure.

As the Lias in this county is a very bad material for economical purposes, it is not often extensively quarried; and, considering the few available sections, the number and variety of organic remains which have been, from time to time, collected, are really remarkable, and show the prolific nature of the sea of that period. Some localities in that sea, of course, would be richer than others, as is the case in the present day; but, on the whole, this formation is everywhere marked by a great abundance and diversity of fossils. The Palæontologist often looks with a longing eye at some old quarry, long since closed, which had been at one time famous for its zoological contents, and speculates upon the wonders which lie concealed beneath his feet; and he restores in thought some ancient monster of the deep, some curiously-formed shell, or some strange plant; and perhaps, if he had the power, he would dig away, in the hope of possessing some of these treasures which his imagination has conjured up before him. And yet, after all, such speculations are not so imaginative or unreal as they may at first sight appear, for the strange and extraordinary forms of extinct life, which the extended researches of scientific inquirers have brought to light, seem to justify the highest flights of fancy; and none can tell when or where some wonderful relic of the past may be found.

A notice of the geology around Killarney having already appeared in the Geologist, by “A Brother of the Hammer,” it will be sufficient for us to indicate the best localities for sections and fossils, premising that the upper and lower Old Red Sandstone are unequivocally represented in Ireland, independently of the upper groups of conglomerates, and red and yellow sandstones.

The Old Red Conglomerate in Ireland is in many places unconformable to the Old Red Sandstone, and constitutes the base of the carboniferous deposits; and I had been assured that the same unconformability had been detected in the Forest of Dean; but a careful examination, with Dr. Melville, has since convinced me that there is no such unconformability between the Upper Brownstones and the overlying masses of conglomerates and red and yellow sandstones in this or the Blorenge district. In Ireland the local geologists persist in limiting the term Old Red Sandstone to a series of deposits which there, most certainly pertain more to the carboniferous group, viz., the conglomerates, red sandstones, and yellow and grey sandstones, which pass upwards conformably into the Coonahola grits and carboniferous slates. The equivalents of our cornstones and brownstones of Brecon and Monmouth may be studied at Glengariff, at the head of Bantry Bay, where the lowest rocks seen are the Glengariff grits, or upper cornstones, overlaid by the Dingle slates or brownstones, and the red sandstones of the conglomerate series, with no unconformability.

Dr. Phipson, of Paris, has drawn attention, in the April number of the Geologist, to the observations which have been made of the presence of mercury in the soil and substrata of the town of Montpellier, and, in your June number, another correspondent notices the finding of the same metal under circumstances so decidedly adventitious, however, as to possess, I think, rather archæological than geological interest. The occurrence of this precious metal in rocks and mineral deposits of such ages as we should hesitate to assign for its matrix, most probably arises from its fluid nature admitting of its easy transport to distances far remote from those formations in which it exists in situ; and, as furnishing something like the history of its presence in such apparently abnormal situations, the following account of its discovery at Ajaccio, in the Island of Corsica, may, perhaps, be considered worthy of insertion:—

In the year 1811, a M. Matthieu, an Engineer Officer of the French Army, was entrusted by Napoleon with the mineral survey of the Island, but, being re-called to his military duties in 1814, was cut off before Leipzig, leaving in the possession of his widow the notes he had made of his survey. These notes do not appear ever to have been officially communicated, but among them was a memorandum to the effect that a deposit of mercury existed at Ajaccio.