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 upon 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 striæ 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 be fore 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 Peatland 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.

2. Zone of Posidonia Bronnii.-This the author divides into several. a. Zone of Am. bifrons.-Containing bands of cement stone.

B. Zone of Am. communis.-Constituting the alum-shale, and characterized throughout by Leda ovum.

7. Zone of Posidonia Bronnii proper, which includes the jet-bearing beds. These form the Upper Lias.

3. Zone of Am. spinatus.-This consists of numerous ironstone bands, which form the workable beds of Yorkshire.

4. Zone of Am. margaritatus.--More micaceous beds.

These two zones are not clearly separable, both Ammonites being found in each.

5. Zone of Am. Darai.-This Ammonite is very rare, if found at all, in Yorkshire, and the zone is more characterized by Am. capricornus.

6. Zone of Am. Ibex.-This form is now recognized for the first time in Yorkshire, but the associated Ammonites, Henleyi and fimbriatus, form a well-marked zone. 7. Zone of Am. Jamesoni.-The true form only found in situ north of Whitby; but the allied brevispina is highly characteristic of the beds, which are very fossiliferous. 8. Zone of Am. armatus. This is well represented; the Pinna folium is conterminous with the two last zones, which end the Middle Lias.

The last four zones are similar in lithological character, being shaly beds with scattered dogger bands.

The zones below this are only seen at Robin Hood's Bay and Redcar.

9. Zone of Am. raricostatus.—This is well developed in micaceous shaly beds, indurated at the top, which is the character also of all the succeeding zones.

10. Zone of Am. oxynotus.—Also well developed, containing a strong limestone band.

11. Zone of Am. Turneri.-Is only found on the shore.

12. Zone of Am. obtusus.-Seen at Peak.

13. Zone of Am. Bucklandi.—Forms the lowest beds seen at Robin Hood's Bay, and the highest at Redcar. They do not contain limestone as elsewhere. An ichthyosaur has been found in these, such having been hitherto only announced from the Upper Lias in Yorkshire.

14. Zone of Am. angulatus.-This is represented by thin shaly beds at Redcar, where this Ammonite is abundant; and also by a limestone-bed near Market Weighton, at which latter place it contains a new and varied fauna.

15. Zone of Am. planorbis.-Hitherto only washed up from the sea in fragments. Its beds have now been discovered near Market Weighton, where they contain numerous foraminifera. In this locality the oyster-bands and white lias are reached, but not the bone-bed.

The lithological character and the position of all these zones were described in the paper.

List of Ammonites in the Author's Cabinet from the several Zones. Those marked P have not been found in situ, but their belonging to the zone is almost certain; those marked p probably belong to the zone.

On the Silurian Rocks of the South of Scotland. By D. J. BROWN. This paper was illustrated by a map and section, also specimens of rocks and fossils.

In a section drawn from Moffat Water in Dumfriesshire to Kilbucho in Peebleshire, we have, first, the Moffat rocks, which consist of hard blue grit (Greywacké) and shale. These are accompanied by beds of anthracite and black shale containing Graptolites; on leaving Moffat Water, we first meet anthracite beds, then a series of grit and shale; this order is repeated six times. The last time we see anthracite beds is at Holmes-water-head, where we find them plunging under the limestone and conglomerate of Wrae and Glencotho, over the whole length of the section from Moffat Water to Holmes Water. The beds stand at a high angle, and have an almost uniform northernly dip. From Holmes Water to Kilbucho the rocks are of a more diversified character. We have first a coarse angular conglomerate, then a bed of limestone with fossils, mostly of a Caradoc type; next a series of beds of slate, shale, and grit; these beds come up again at Kilbucho. After Holmes Water we have no longer the uniform northernly dip, but the beds undulate, and in one section are seen to form regular waves.

These beds all along the line of the section, from the river Tweed to Kilbucho, are given in the Government Geological Map of Peebleshire as one series of Llandeilo age. The author is of opinion that they form two series—a lower Moffat or Llandeilo, and an upper or Caradoc series that lies unconformable upon the lower. The author has come to the conclusion that the two series are unconformable:First, because we find the anthracite beds at a high angle plunging under the limestone and Conglomerate of Glencotho and Wrae at Holmes-water-head, and emerging at the same angle in the Moor-foot Hills. Second, because we find these upper rocks everywhere underlaid by a bed of coarse angular Conglomerate; and this conglomerate is found in fragments, and nowhere in situ, in the neighbourhood of Moffat, which is on the opposite watershed, being, as the author thinks, fragments of the lower rocks left in the process of denudation. Third, this Conglomerate is found to contain numerous fragments of anthracitic shale containing Graptolites belonging to lower beds, proving that the lower rocks were consolidated, and then torn into fragments before the upper rocks were laid down.

On the Upper Silurian Rocks of the Pentland Hills and Lesmahago.
By D. J. BROWN.

This paper was illustrated by a map and two sections.

In a paper published in the Transactions of the Edinburgh Geological Society, vol. i., written by Mr. Henderson and the author, it was shown that in the North Esk section of the Pentland Hills there is a very perfect Wenlock fauna, and that it is only towards the top of the section that the Ludlow species come in; it was further shown, from Silurian fossils collected from the Red Conglomerate lying at the top of the section, that these Red Conglomerates were not a part of the Lower Old Red Sandstone, but a continuation of the Silurian, and that the whole Silurian rocks in the Lyne water form a continuous section above them. In the district of Lesmahago the Upper Silurians are said to form a continuous series with the Lower Old Red Sandstone that lies above them. In "Memoir 32, Geological Survey of Scotland," the same phenomena are said to occur in the Pentlands, and Mr. Salter draws a parallel between these beds and those of Lesmahago; but from this comparison he omits the section in the Lyne water, which forms a continuous series above the Red Rocks, said to be Old Red Sandstone, so that these Old Red Sandstone beds of the Government Survey lie right in the centre of the continuous section of Upper Silurian, and contain Upper Silurian fossils. As it is only towards the top of the North Esk section that we find any fossils belonging to the Lesmahago beds, and they differ from them very much in their lithological character, the author is of opinion that these beds are not the equivalent of the Lesmahago beds but that these latter form an upper series overlying the Pentland beds.