Upon commencing, in 1847, the special study of the igneous rocks, I, no doubt in common with many others, took for granted the conclusions arrived at experimentally by Professor Bischof, of Bonn, as to the amount of contraction which such rocks would undergo when passing from the state of hot liquidity to that of cold solidity; and I did so, not after any critical examination of the details of Bischof's inquiry itself (the most important of which are contained in a memoir published in Leonhard und Bronn's Jahrbuchfor 1841), but merely in deference to authority, since these conclusions had apparently received unquestioned acceptation from geologists in general.

Within the last few months considerable, interest has been revived on the question of the origin of certain small excavations or borings which have been found in limestone rocks in different localities in Sicily, France, England, and Wales. The first public notice of them in England was by Dr. Buckland, whose attention, when at a meeting of Geologists at Boulogne in 1839, was called to some borings which had been found in the under-surface of a ledge of Carboniferous Limestone rock in the Boulonnais. After this Dr. Buckland examined some similar borings which the Rev. N. Stapleton had observed near Tenby, and described both caseg, in a communication to the Geological Society in 1841. About the same time that Dr. Buckland was engaged with these excavations, M. Constant Prévost found some similar perforations on Monte Pelegrino, near Palermo. Mr. C. P. Jopling discovered them in Furness in 1843. M. Bouchard Chantereaux, who met with them in the Bois des Roches, in the Bas Boulonnais, has published a memoir on the subject, the result of many years observation, to which I shall have occasion again to refer. Mr. Pengelly met with them in many localities in the Torbay district. They were also found on Birkrigg Common by Miss E Hodgson, of Ulverston, and were described by her in vol. vii of The Geologist, p. 42.

We have now, I think; obtained sufficient evidence that the disposition of differently coloured or composed bands in agate is in most cases the result of crystalline segregation.We shall find, also, that the order of this segregation is constant under given conditions; and that, with fixed proportions of elements and fixed rate of cooling and drying, the agate will necessarily produce itself in a riband of a fixed succession or pattern of stripes: a spectrum of substances, which, if we had observed data enough, we might read like a spectrum of light; inferring, not the nature of the elements from its bars of colour, but the: former conditions of solution from the bars of elements.

An interesting Article by my colleague, Mr. C. E. De Rance, in the last number of this Magazine, upon “The Surface-Geology of the Lake-District,” induces me to offer a few remarks in connection with the subject.

The Article in this Magazine by Prof. Harkness, “On the Middle Pleistocene Deposits of Britain,” will, I trust, call the attention of geologists more prominently to the fact that a break occurred in the Glacial period, wherein the formation of Boulder-clay was arrested for a considerable interval, and an extensive formation of sands and gravels spread out, accompanied, apparently, by some amelioration of the temperature of the sea. Nevertheless, there are several things pressed by Prof. Harkness into his case as to which a word of caution, and even of dissent, seems necessary.

The Paper “On the Formation of the Chesil Bank,” which appeared in the GEOLOGICAL MAGAZINE for October last, is prefaced by a statement that the authors (Messrs. Bristow and Whitaker) do not propose to enter into the question of the way in which the shingle was heaped up. But the way in which the shingle was heaped up is intimately connected both with the formation of the Chesil Bank and with its position in advance of the shore line, and, if rightly understood, any speculations on the waste of the coast behind the bank by sub-aerial denudation are superfluous.

In the article on Terraces in your last number, Mr. G. Poulett Scrope evidently did not intend writing in a style that would bear being minutely criticized, or he was not sufficiently particular in quoting from my work and representing my present views. As it stands, a reader of Mr. Scrope's article would receive impressions very different from those which a perusal of my chapter on Raised Beaches and Inland Terraces would leave on his mind. Such being the case, I am sure Mr. Scrope will pardon me if I make a few remarks in self-vindication.