where X represents a base containing two atoms of hydrogen more than morphia (i. e. = C1, II, NO,), and Y a base containing one atom of oxygen less than X (i.e. = CH NO). Simultaneously with the production of these substances, iodide of methyl, in quantity representing almost exactly of the carbon in the codeia used, is evolved.

21

By allowing the action of 10 parts codeia, 30 of 55 per cent. hydriodic acid, and 3 of phosphorus, to take place at 100°, a compound is produced separable from the viscid liquid resulting from the reaction by addition of water, washing, and drying at 100, and representing in constitution the formula

If, however, the reaction take place at a somewhat higher temperature, a similar body containing two molecules of water less is formed,

4X + 6III – 2H, O = C, H, I, N, O10, 4HI;

68 82

whilst if the mixture be allowed to boil rapidly, so as to distil off most of the excess of hydriodic acid employed, and ultimately raise the boiling-point to 130° or upwards, the product contains four atoms of oxygen less than this last compound, being

=

4Y+6HI-211, O C, H, I, N, O, 4III.

68 82 2

Simultaneously with these bodies much phosphorous and phosphoric acids are produced.

On dissolving these substances in hot water and cooling, there are obtained products apparently crystalline to the eye, but under the microscope consisting of coalesced globules only. In this way the following bodies have been obtained:

The free bases of some of the foregoing hydriodates have also been obtained. They oxidize very readily, forming orange-coloured substances that ultimately become black.

Finally, by the action of hydriodic acid on the three bodies of the formulæ last given, the elements of III and also of H, O are taken up; the following compounds having been thus obtained,

The H2O thus taken up remains firmly united to the body of the molecule, exposure to a temperature of 100° for days not driving off any water.

In qualitative reactions, all these bodies are very similar: alkalies throw down a white precipitate of variable composition in the case of those bases which contain iodine united to the molecule of base. In all cases this white precipitate rapidly becomes yellow, orange, and finally brown, oxygen being absorbed. In water and sodium carbonate these precipitates are but little soluble; in ammonia, and especially caustic potash, readily soluble.

Oxidizing agents (e. g. nitric acid) produce a bright yellow or orange-yellow

tint.

In most of the above reactions, this set of compounds differs much from those got by the action of hydrochloric and hydrobromic acids; the free bases of these latter derivatives having a tendency to become green by oxidation in the air, and yielding red or purple colorations with oxidizing agents.

The codeia used in the experiments above described formed part of a large supply, exceeding twenty ounces, most liberally presented for the purpose by Messrs. J. F. Macfarlane and Co., of Edinburgh.

GEOLOGY.

Address by ARCHIBALD GEIKIE, F.R.S., President of the Section. INSTEAD of offering to the Geological Section of the British Association an opening Address on some special aspect or branch of general Geology, I have thought that it might be more interesting, and perhaps even more useful, if I were to lay before you an outline of the geology of the district in which we are now assembled. Accordingly, in the remarks which I am now about to make, I propose to sketch to you the broader features of the geological structure and history of Edinburgh and its neighbourhood, dwelling more especially on those parts which have more than a mere local interest, as illustrative of the general principles of our science.

It would be as unnecessary as it would be out of place here to cite the long array of authors who have each added to our knowledge of the geology of this district, and many of them also, at the same time, to the broad fundamental truths of geology. And yet it would be strange to speak here of the rocks of Edinburgh without even a passing tribute of gratitude to men like Hutton, Hall, Jamieson, Hay Cunningham, Hibbert, Hugh Miller, Fleming, Milne Home, and our late esteemed and venerable associate, Charles Maclaren-men who have made the rocks of Edinburgh familiar to geologists all over the world. If, therefore, I make no further allusion to these and other names, it is neither that I forget for a moment their claims, nor that I now bring forward any new material of my own, but because I wish to be understood as dealing with facts which, thanks to the labours of our predecessors, have become part of the common stock of geological knowledge. For the purpose of gaining as clear an idea as may be of the rocks among which Edinburgh lies, and of the way in which they are grouped together, let us imagine ourselves placed on the battlements of the Castle, where, by varying our position, we may obtain a clear view of the country in every direction for many miles round. To the south-east the horizon is bounded by a range of high ground, rising as a long tableland above the lowland of Midlothian. That is a portion of the wide Silurian uplands of the south of Scotland, forming here the chain of heights known as the Lammermuir and Moorfoot Hills. Along most of its boundary line, in this district, the Silurian tableland descends with tolerable rapidity towards the plain, being bounded on its north-west side with a long fault, by which the Carboniferous rocks are brought down against the hills. These Silurian rocks are the oldest strata of the district; and it is on their contorted and greatly denuded beds that the later formations have been laid down.

The Pent

Turning now to the south, we see the chain of heights known as the Pentland Hills, striking almost from the very suburbs of Edinburgh south-westward in the direction of the Silurian uplands, which they eventually reach in the county of Lanark. This line of hills rises along an anticlinal axis by which the broad Carboniferous tract of the Lothians is divided into two distinct portions. lands themselves consist, as I shall afterwards point out, chiefly of rocks of Old Red Sandstone age; but the anticlinal fold along which they rise is prolonged through the Braid Hills, and through the Carboniferous ground by the Castle Rock of Edinburgh, even as far as the opposite shores of Fife. From the Castle we can readily follow with the eye the effects of this great dominant fold of the rocks. To the east, we mark how the strata dip away eastward from the axis of movement, as is shown in the escarpments of Salisbury Crag, Arthur's Seat, and Calton Hill, while on the opposite or western side the escarpment of the wooded hill of Corstorphine, facing towards us, points out the westward dip. From the same standpoint we can even detect the passage of the arch into Fife; for the rocks about Aberdour are seen dipping to the west, while eastward they bend over and dip towards the east at Kinghorn.

Although the structure of the district is simple when the existence and position of this anticlinal axis is recognized, some little complication is introduced by a long powerful fault which flanks the axis on its south-eastern side. The effect of this fault is to throw out a great part of the lower division of the Carboniferous formations, and to bring the Carboniferous Limestone series in some places close.

against the Lower Old Red Sandstone and its volcanie rocks. Another result has been the extreme tilting of the strata, whereby the Limestone series along the east side of the fault has been thrown on end, and even in some parts bent back into a reversed dip. Hence, while on one side of the axis the Limestone series is sometimes only a few hundred yards distant from the Old Red Sandstone, on the opposite or north-west side the distance is fully eleven miles, the intervening space being there occupied by endless undulations of the lower divisions of the Carboniferous system. Hence, too, the Millstone-grit and Coal-measures come in along the centre of the Midlothian basin a short way to the east of the Pentland axis; while on the west side they are not met with till we reach the borders of Stirlingshire and Linlithgow.

Another remarkable and readily observable feature is, that on the west side of the Pentland ridge the Carboniferous formations, from almost their base up to the top of the Carboniferous Limestone series, abound in contemporaneous volcanic rocks; while on the east side, beyond Edinburgh and Arthur's Seat, such rocks are absent until we reach the Garlton Hills, to the north of Haddington, where they reappear, but in a very different type from that which they exhibit to the west. Let us now pass in review the different geological formations which come into the district around us, beginning with the oldest and ascending through the others till we reach the superficial accumulations, and mark, in conclusion, how far the present surface-features are connected with geological structure.

[The author then described the various geological formations of the districtSilurian, Old Red Sandstone, and Carboniferous-dwelling in particular upon the history of volcanic action in that part of Scotland. On this subject he remarked :—]

Outline of the History of Volcanic Action around Edinburgh.

The oldest volcanoes of this part of Scotland were those which, during the time of the Lower Old Red Sandstone, poured out the great sheets of porphyrite and the showers of tuff which now form the main mass of the range of the Pentland Hills. During the same long geological period volcanic action was rife, as we have seen, along the whole of the broad midland valley of Scotland, since to that time we must refer the origin of the Sidlaw and the Ochil Hills, part of eastern Berwickshire, and the long line of uplands stretching from the Pentland Hills through Lanarkshire, and across Nithsdale, far into Ayrshire.

Of volcanic action, during the remainder of the Old Red Sandstone period, there is around Edinburgh no trace. But early in the following or Carboniferous period, the volcano of Arthur's Seat and Calton Hill came into existence, and threw out its tiny flows of basalt and porphyrite, and its showers of ashes. From that time onwards, through nearly the whole of the interval occupied by the deposition of the Carboniferous Limestone series, the district to the west of Edinburgh was dotted over with small cones, usually of tuff, but sometimes emitting limited currents of different basalt rocks, more especially in the space between Bathgate and the Forth, where a long bank, chiefly formed of such lava-currents, was piled up over and among the pools and shallows in which the limestones, sandstones, shales, and coal-seams were accumulated. To the north, also, similar volcanic activity was shown in the Fife tracts nearest the Forth; while eastwards, between Haddington and Dunbar, there lay a distinct volcanic focus, where great showers of red felspathic tuff and widespread sheets of porphyrite were ejected to form a bank over which the Carboniferous Limestone series was at length tranquilly deposited.

Volcanic activity seems to have died out here before the close of the Carboniferous Limestone period. It remained quiescent during the deposition of the Millstone-grit and Coal-measures; at least no trace of any contemporaneous igneous ejection is found in any part of these formations. The intrusive masses of various basalt rocks, which here intersect the older half of the Carboniferous system, are, in all probability, of Lower Carboniferous date, connected with the eruptions of the interbedded volcanic rocks. The next proofs of volcanic action in this neighbourhood are furnished by the upper part of Arthur's Seat. At that locality we discover that after more than 3000 feet of strata had been removed by denudation from the Pentland anticlinal fold so as to lay bare the old Lower Carboniferous volcanic rocks of Edinburgh, a new focus of eruption was formed, from which

were ejected the basalts and coarse agglomerates of the summit and shoulders of Arthur's Seat. There is no trustworthy evidence for fixing the geological date of this eruption. Evidently, from the great denudation by which it was preceded, it must belong to a much later period than any of the Carboniferous eruptions. Yet, from the great similarity of the Arthur's Seat agglomerate, both in composition and mode of occurrence, to numerous "necks" which rise through all parts of the Carboniferous system between Nithsdale and Fife, and which I have shown to mark the position of volcanic orifices during Permian times, I am inclined to regard these later igneous rocks of Edinburgh as dating from the Permian period. Arthur's Seat, however, seems to have been the only volcano in action during that period in this neighbourhood.

There still remains for notice one further and final feature of the volcanic history of this part of Scotland. Rising indifferently through any part of the other rocks, whether aqueous or igneous, and marked by a singular uniformity of direction, there is a series of basalt dykes which deserves attention. They have a general easterly and westerly trend, and even where, as in Linlithgowshire, they traverse tracts of basalt-rocks, they preserve their independence, and continue as readily separable as when they are found intersecting sandstones and shales. These dykes belong to that extensive series which, running across a great part of Scotland, the north of England, and the north-east of Ireland, passes into, and is intimately connected with, the wide basaltic plateaux of Antrim and the Inner Hebrides. They date, in fact, from Miocene times, and, from their numbers, their extent, and the distance to which they can be traced from the volcanic centre of the north-west, they remain as a striking memorial of the vigour of volcanic action during the last period of its manifestation in this country.

Glacial Phenomena.

To an eye accustomed to note the characteristic impress of ice-action upon a land-surface, the neighbourhood of Edinburgh presents many features of interest. It was upón Corstorphine Hill, on the western outskirts of the city, that Sir James Hall first called attention to striated rock-surfaces which, though erroneously attributed to the abrasion produced by torrents of water, were even then recognized as trustworthy evidence of the last great geological changes that had passed over the surface of the country. Even before we come to look at the surface in detail, and note the striation of its rocks, we cannot fail to recognize the distinctively iceworn aspect of the hills round Edinburgh. Each of them is, in fact, a great roche moutonnée, left in the path of the vast ice-sheet which passed across the land. That this ice was of sufficient depth and mass to override even the highest hills, is proved not merely by the general ice-worn surface of the landscape, but by the occurrence of characteristic striae on the summits of the Pentland Hills, 1600 feet above the sea; that it came from the Highlands, is indicated by the pebbles of granite, gneiss, schist, and quartz rock occurring in the older boulder-clays which it produced; and that, deflected by the mass of the southern uplands, the ice in the valley of the Lothians was forced to move seawards, in a direction a little north of east, is shown by the trend of the striæ graven on the rocks, as at Corstorphine, Granton, Arthur's Seat, and Pentland Hills.

Connexion of the present form of the Surface with Geological Structure.

In concluding these outlines, let me direct the attention of the Section to the bearing which the geological structure of the district wherein we are now assembled has upon the broad and much canvassed question of the origin of landsurfaces. In the first place, we cannot fail to be struck with the evidence of enormous denudation which the rocks of the district have undergone. Every formation, from the oldest to the latest, has suffered, and the process of waste has been going on apparently from the earliest times. We see that the Lower Silurian rocks were upheaved and denuded before the time of the Lower Old Red Sandstone; that the latter formation had undergone enormous erosion before the beginning of the Carboniferous period; that of the Carboniferous rocks, a thickness more than 3000 feet had been worn away from the site of Arthur's Seat before the last eruptions of that hill, which are possibly as old as the Permian period

that still further and vaster denudation took place before the setting in of the Iceage; and finally, that the deposits of that age have since been to a large extent removed. With the proofs, therefore, of such continued destruction, it would be vain to look for any aboriginal outline of the surface, or hope to find any of the later but still early features of the landscape remaining permanent amid the surrounding waste.

In the second place we note that, in the midst of this greatly denuded area, it is the harder rocks which form the hills and crags. Those masses which in the long process of waste presented most resistance to the powers of destruction, are just those which, as we might expect, rise into eminences, while those whose resistance was least sink into plains and valleys. All the craggy heights which form so conspicuous a feature of Edinburgh and its neighbourhood, are composed of hard igneous rocks, the undulating lowlands lie upon soft aqueous rocks.

In the third place, the coincidence of the position of hills and crags with the existence of ancient igneous rocks, cannot be misinterpreted by ascribing the presence and form of the hills to the outlines assumed by the igneous material ejected to the surface from below. The hills are not due to igneous upheaval at all, but can be shown to have been buried deep under subsequent accumulations, to have been bent and broken with all the bendings and breaks these later formations underwent, and to have been finally brought to light again only after a long cycle of denudation had removed the mass of rock under which they had been concealed. What is true of the hills of Edinburgh, is true also of all the older volcanic districts o Britain. Even where the hills consist of volcanic rocks, their existence, as hills, can be proved to be one of the results not of upheaval but of denudation.

In the fourth place, this district furnishes an instructive illustration of the influence of faults upon the external contour of a country. The faults here do not form valleys. On the contrary, the valleys have been cut across them in innumerable instances. In the Dalkeith coal-field, for example, the valleys and ravines of the river Esk traverse faults of 190 to nearly 500 feet, yet there is no inequality at the surface, the whole ground having been planed down by denudation to one common level. When, however, a fault brings together rocks which differ much in their relative powers of resistance to waste, the side of the dislocation occupied by the harder rocks will tend to form an eminence, while the opposite side, consisting of softer rocks, will be worn down into a hollow or plain. Conspicuous examples are furnished by the faults which, along the flanks of the Pentland Hills, have brought down the comparatively destructible sandstones and shales of the Carboniferous series, against the much less easily destroyed porphyrites and conglomerates of the Old Red Sandstone.

In fine, we learn here as elsewhere in our country, and here more strikingly than often elsewhere, on account of the varied geological structure of the district, that the present landscape has resulted from a long course of sculpturing, and that how much soever that process may have been accelerated or retarded by underground movements, it is by the slow but irresistible action of rain and frost, springs, ice, and the sea, that out of the various geological formations among which Edinburgh lies, her picturesque outline of hill and valley, crag and ravine, has, step by step, been carved.

The Yorkshire Lias and the Distribution of its Ammonites.

By the Rev. J. F. BLAKE.

The Lias of Yorkshire is exposed on the coast for a distance of about 30 miles, and owing to faults and undulations the series is repeated twice, one main area being to the north, the other to the south of Whitby; and there are two outlying patches, one of the highest beds at Peak, the other of the lowest beds at Redcar. The basis of the description in this paper is the division into Ammonite zones, as by Oppel and others.

1. Zone of Ammonites Jurensis.-These occur at Peak. The author has not found the characteristic Ammonite in situ, but recognizes the zone by its peculiar fauna. It appears to be divided into an upper and lower division.