We called attention to Part ii. of the Fifth volume of the Journal of this Society in our December number. We have just received the first part of the sixth volume, and are glad to find that the subject of Agricultural Geology once more finds a place in its pages, and that the Secretary, Mr. Jenkins, is again its advocate and exponent. In the present part, Mr. Jenkins applies his geological training to an exposition of the surface-geology of Belgium, whither he had gone in the latter part of the summer of 1869 to report on the Agriculture of that kingdom, accompanied by Dr. Augustus Voelcker, the Society's chemist.

I Have been gratified by observing of late the appearance among geologists of a more general appreciation of the study of volcanic phenomena,—using that word in its broadest sense, as comprehending not merely the occasional outbursts of vapour, ashes, and lava, but also the action of those subterranean forces, to which alone we are indebted for the existence, now or in former times, of any dry land whatever above the dead sea-level at which the agents of denudation would otherwise maintain the surface of the globe.

During one of my last visits to England I had the opportunity of visiting a great number of palsæontological collections. Amongst those which afforded me the greatest pleasure, I would specially mention the collections of Mr. Edward Wood, F.G.S., at Richmond, in Yorkshire, and of Mr. John Gray, at Hagley, near Stourbridge.

In his description, Brocchi does not fail to observe that this is a very variable species. It is more or less transverse or elongated, and while some specimens are entirely smooth, others present from two to four ribs near the front in both valves, and about a similar number on each of the lateral portion of the shell, but these ribs are short and do not seem to extend far in the direction of the beaks. The ventral valve is gibbous, with a well-defined fold, while in the dorsal valve the sinus is broad and deep. In Brocchi's typical form the shell is smooth, while to the more or less plicated specimens Costa has applied the specific name oi plieato-dentata, but, as was well shown by Philippi (Enum. Moll. Sicil., vol. 2, pi. xviii., fig. 5, 1844), there exists every passage in shape between the more transverse and smooth specimens to those that are more elongated and plicated near their margin. Rh. bipartita is also stated by Meneghini and others to occur in the Middle (?) and Upper Miocene, as well as in the Older Pliocene.

The outlying mass of Lias on the borders of Shropshire and Cheshire is so thickly covered with Boulder-drift, that its line of boundary throughout almost its entire circumference is very obscure. The direct sequence from the underlying Keuper Marls is scarcely anywhere visible, and I believe no record of the occurrence of the Avicula contorta zone has hitherto been published.

The transition or passage-beds between any two large formations are always difficult to make out, and those between the Old Red Sandstone and the Silurian are no exception to the rule. Much light has recently been thrown upon the latter, yet much more is needed before the exact order and position of their different beds can be considered as finally decided.

For many years past I have, at intervals, devoted attention to Tertiary Brachiopoda, and I now propose to note down some remarks in connection with those of Italy.

In Professor Harkness's very interesting paper “On the Middle Pleistocene Deposits,” he alludes to the beds described by Mr. George Maw, “in the valley of the Severn, between Bridgenorth and Shrewsbury, which seem to accord with the shell-bearing beds of Ireland”

The sandstone beds which skirt the eastern border of Wales, and stretch from a little south-west of the town of Oswestry to near the Point of Ayr, on the shores of the Irish Sea, a distance of upwards of 40 miles in a direct line, have for several years past been a source of perplexity to those who have investigated their peculiarities, and who have been interested in arriving at a determination of their true age and geological horizon.

The Chalk from Cop-point, near Folkestone, to Walmer in Kent, has been so well described by Mr. W. Phillips, that I need do little more than allude to his paper, in reference to the divisions of the Chalk in East Kent; but in a notice of the Isle of Thanet by the Rev. W. D. Conybeare, this gentleman, from the absence of flints in the Chalk near Margate, was led erroneously to suppose it to belong to the lower division, and it was not till 1865 that this error was exposed in a paper on the Chalk of the Isle of Thanet by Mr. W. Whitaker, F.G.S., of the Geological Survey, the latter gentleman pointed out the true position of the Margate Chalk, as that of the highest Chalk, and superior to that with numerous flints seen at Ramsgate; and he there remarked, “Very likely the Broadstairs Chalk will turn out to be the upper part of the ‘Chalk with many Flints’ (Phillips) of the cliffs from Walmer Castle to Dover Castle, and which is there the highest division; so that the Isle of Thanet section would be the upward continuation of that given by Mr. Phillips.”

In the British Museum there is the right ramus of the mandible of a young Palœotherium magnum, obtained by M. Bravard from the Eocene strata of Vaucluse, which possesses a peculiar interest, inasmuch as the three principal milk molars are completely cut, though their unworn crowns show that they have not long been, in place. The ramus itself must have been nearly eight inches long when it was complete, while the distance from the articular surface of the condyle to the lower margin is about 3·25in. The symphysial surface is oval, rugose, and extends back nearly as far as the anterior margin of the crown of the first visible grinder; the anterior, or mental region of the ramus, is inclined upwards and forwards, and is slightly convex, as in all the true Palœotheria. In front of the most anterior milk molar which is in place, there is an oval fossa about 0·2in. long, which appears to lead into the alveolus of the proper first milk molar (dm1); and further forward (but not more than 0·2in., so that the diastema of the milk teeth must have been exceedingly short) a series of depressions on the truncated anterior end of the ramus represent the bottoms of the alveoli of the canine and incisors.

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.

During a brief visit in Devonshire, the main outlines of the features of the country appeared due to ice sculpture; nevertheless, the vast amount of denudation observable among the hills, evidently the result of meteoric abrasion, caused me to be cautious in coming to a conclusion too quickly, although Mr. G. W. Ormerod, F.G.S. (whose minute knowledge of the district is well known, and with whom I had the pleasure of examining a part of Devon), pointed out that in various places he had found glacier-formed drift. Having subsequently visited both Devon and Cornwall, although time did not permit of a minute search for ice-striæ, yet seemingly the first-formed impressions were correct, and, apparently, ice was the principal agent employed to carve out the main features of this portion of England.

Little as the Geology of South America has been worked, yet the presence of coal along the coast of Chile has long been known to navigators and others. Of late years this coal has been worked in sundry places—in short, wherever the circumstances seemed most favourable. The strata in which the seams occur, were made the subject of considerable study from a palæontological point of view by D'Orbigny and by Darwin; but not until the last ten or fifteen years have the resources of the country, with regard to this branch of industry, been examined into sufficiently to enable a correct estimate to be made of them. The surveys, which have been the direct result of the interest awakened by the knowledge of the presence of workable seams of lignite in Chile, have been greatly conducive to a more perfect knowledge of the geological structure of the coast; and the consequent accumulation of material for its study has, we believe, brought it within our power, not only to add to the very limited stock of notes on the subject, but also, it is hoped, to give such explanations of some of the more obscure facts connected therewith as were, from the want of reliable data, either overlooked by earlier observers, or only vaguely suggested by them.

There is, perhaps, no question of greater interest in the whole A range of physical geography than the circumstances that have determined the existence on the earth's surface of large and comparatively unbroken areas of land and water, involving as it does the debateable subject of marine and sub-aerial denudation, and the careful weighing of evidence on the just apportionment of these operations and of oscillations of level that have brought about the existing boundaries of sea and land.

In replying to Mr. Forbes” strictures upon my paper at Cambridge upon “The elevation of Mountains, etc,” I may be permitted to say, what would otherwise be of no consequence. The paper was read in April 1868. I received it back from the referees, accompanied by some valuable suggestions, in September. I was at that time much occupied, and did not work out those suggestions until January 1869. After having done so I wrote to Mr. Forbes, received his reply on the 29th, and a week later sent the paper back to the referees.

Since I first saw my short notice on “Faults in Strata” in print (GeologicalMagazine, 1869, Vol. VI., p. 341), I have been anxious to remove a blemish of apparent flippancy in alluding to systems as applied to faults. I had indeed in view cases where that method had been used imitatively—with the tacit assumption of an established and well-understood meaning; but I lost sight of the fact that serious special work had been devoted to the subject, and my remark was unqualified. I have to thank my friend Mr. W. T. Blanford for an opportunity of making this correction, as well as of adding some further considerations on so important a point in the principles of stratigraphy.

The Lower Silurian rocks of Scotland, largely developed as they are in the south, and in spite of the great labour that has been bestowed upon them, are by far the least known of all the fossiliferous formations of that country. While the maps of the Government Geological Survey are coloured in all the subdivisions of the strata of the other formations included in their area, the Lower Silurians are merely indicated by a common purple tint, and not the slightest attempt at a subdivision is made. Even the single bed of Limestone they contain, below the horizon of that of the W. coast, is doubtfully referred to the Llandeilo, and the sign of interrogation is carefully placed before its title. Nicol, Harkness, J. C. Moore, and many other eminent geologists, have worked different portions of these ancient deposits since the publication of “The Silurian System,” but as yet very little progress has really been made in correlating its different parts with those of the type formation of the sister country.

The forms which Mr. Davidson in his invaluable Monograph has included under T. ovoides, are so various that it would be possible to refer the shells figured in the plate to that species, but since T. trilineata, from the Inferior Oolite, and T. lata and T. ovoides, from drift-blocks—which I shall endeavour to show are of the very latest Jurassic horizon—are very different in many respects, I prefer to give a new name to this form, which may find its place near T. ovoides and T. simplex. The specimen drawn, Fig. 1 and la, is from the collection of Mr. Roper of Lowestoft, who obtained it, with another specimen, from a gravel-pit at Thorpe in Suffolk. It has the general simple form of T. ovoides, but is remarkable for its great size. The imperforate valve is flattened in the mesial line, whilst the perforate valve is deep and raised into a well-pronounced keel in the mesial line extending from the beak; the foramen is small. The specimen figured is longer than the other in Mr. Roper's collection, which has the shorter, squarer form of Fig. 2, resembling T. simplex. This fine Terebratula may be known as T. rex.

The number of Scientific Opinion for October 27 (page 457), contains a note by the Rev, Osmond Fisher, calling attention to a suggestion, with regard to the liquefaction of deeply buried rocks, made by him in a paper read before the Cambridge Philosophical Society in April, 1868, and since published in the Transactions of that Society. In a notice of this paper by him, in the Geological magazine for November, 1868, Mr. Fisher insists that deeply buried and intensely heated portions of rock, which, in accordance with the conclusions of Mr. Hopkins, are kept in a solid state by great pressure, may, by a diminution of pressure consequent upon movements of the earth's crust, assume a liquid condition, and thus give rise to lavas. This suggestion is however claimed by Mr. Scrope, in a communication to the same Magazine for December, 1868, as his own, and as having been put forward by him in both editions of his now classic work on Volcanos. This statement of Mr. Scrope was questioned by Mr. Fisher in the Geological magazine for January, 1869, and Mr. Scrope does not appear to have replied. In a paper in the same magazine for June, 1869, I have referred to this view as belonging to Mr. Scrope, and as also advocated by Mr. Fisher, who has availed himself of the republication of my paper in Scientific Opinion for October 20, to re-assert his claim to be the originator of this view, and to demand either of Mr. Scrope or myself some justification of our assertions.