group. Across that portion of Scotland, immediately to the north of the district at present under consideration, we have part of the same sequence, commencing with the Lias. This formation at Cromarty is considerably to the west of the first appearance of the same formation in England; but this results naturally from what was before mentioned of the geological formations running not east and west, but north-east and northwest, not right, but diagonally across the country. We have, then, Lias at Cromarty, and a lower Oolite near Elgin. May it not be possible that all we want to complete the remaining members of the series is simply to be able to carry out our section into the Moray Firth? Such a hypothesis receives confirmation from the fact that in the neighbourhood of Elgin are beds containing Wealden fossils, which Nicol says we are led to suspect are not original formations, but fragments of more extended beds, perhaps drifted to this place. The drifted clay containing Lias fossils at Blackpots may also indicate a formation beneath the waters of the bay. By referring to the Geological Map of England, it will be seen that the greensand accompanies the chalk on the west, and on the east the Lias, &c., to the shore of the channel. Our patch of it at Cruden might form part of the termination of a similar strip, unless it too may be accounted for in the same way as the Moray Wealdens, by supposing it a drifted fragment from the north. May we then fairly infer that at one period the space now occupied by the Moray Firth contained a perfect sequence of the secondary formations ;-that first the soft chalk strata suffered denudation by the ordinary action of north-easterly gales, and that the roll of the German Ocean, piled up its waterworn flint boulders along its successive ancient shores; and that the Wealdens and Oolite of Elgin and the Lias of Blackpots followed in the same course? That part of this theory applicable to the Lias of Blackpots Mr Miller states thus:-"There had probably existed to the west or north-west of the deposit, perhaps in the midst of the open bay, formed by the promontory on which it rests (for the small proportion of other than Liassic materials, which it contains seems to show that it could be derived from no great distance), an out-lier of the lower Lias. The iceberg of the cold Glacial period, propelled along the submerged land by some Arctic current, or caught up by the Gulf-stream, gradually grated it down, as a mason's labourer grates down the surface of the sandstone slab he is engaged in polishing; and the comminuted debris, borne eastward by the current, was cast down here." At Blackpots the Lias fossils occur in clay containing few other boulders. At Boyndie, further west, flint boulders are pitched up on the shore. And at Delgaty, ten miles inland, they occur in great abundance, along with boulders of quartz rock, but no fossils except their own. It would therefore appear that we owe the flint boulders and Lias boulders to different periods. And as the chalk overlies the Lias, it may be that its denudation was completed, and its fossils thrown up on the high grounds of the interior previous to the formation of the boulder clay containing the fossils of the Lias. Although not in this locality, as far as we know, yet in other places (as on the banks of the Thurso in Caithness) the boulder-clay has been found to contain fragments of chalk flints, and also a characteristic conglomerate of the Oolite, as well as comminuted fragments of existing shells." These facts seem also to favour the hypothesis just stated. Since I wrote first on this subject more attention has been paid to the pleistocene deposits in the locality with which we have been dealing. I am not aware that any new facts have been elicited regarding the topics I have made our subject to-night, and I feel that the question altogether is one involved in considerable darkness, and that it is vain to attempt any generalisation upon it till the local geology has been far more accurately examined and determined. To this end the yearly labours of Mr Thomas F. Jamieson of Ellon are devoted, and each season adds more or less to our knowledge of the country. What a curious jumble we have in that out-of-the-way corner of the world! Rock-bound coasts of frowning granite, slates and porphyries, slips of Old Red Sandstone, patches of greensand and red crag, Wealden and Lias and chalk fossils, and all, as we say down there, pretty much "cardid thro' ither," that is, mixed up promiscuously. Ere the Gordian knot be untied, much of interest to the geologist, both scientific and economic, cannot fail to come to light, and the labour which must be expended on the examination will assuredly not be thrown away. 15th March 1877. D. MILNE HOME, Esq., LL.D., President, in the Chair. The following Communications were read:— On Rolled Pebbles from the Beach at Dunbar. By Dr W. T. BLACK. Several banks of corroded pebbles and stones were thrown up on the beaches on the east side of Dunbar, facing the Links, by the late winter gales, brought there probably from more distant localities to the east, and from the greater depths of the sea reached by the waves. These illustrate the beginnings of the formation of larger pebble banks as those of Chesil, and Northam Burrows, by the occurrence of an obstruction to the surge of the wave by the perpendicular face of the bank of turf of the Links, causing a bed of pebbles to be deposited at the base in front, and again on its summit behind. The pebbles seem as if their rounded ovoid shape were due to like actions as produce the ovoid shape of a cake of soap after much use, viz., a sliding motion in the palm of the hand, and with an occasional rolling of the mass round. Similarly these pebbles are first rolled up the slope of the bank by the impact of the surge towards the crest, whence again they descend by sliding within amongst themselves, influenced chiefly by the action of gravity, and lubricated by the return wash. The ovoid shape seems to be taken by all sorts of stones, from the soft sandstone to the hard quartzite, and may therefore be independent of mineral composition, or relative hardness of the stone. The sagittæ of the chords of the rounded surfaces may be assumed to be inversely proportionate to the amount of friction employed in shaping them respectively, i.e. when the sagitta is short greater friction would have been exerted than on that face where the sagitta is longer. Sandy layers are to be seen at the bottom and base of these newly formed pebble banks, as well as on the old ones at Chesil, and Northam, and may be taken to represent the debris of the friction of the stones amongst each other in the mass above. The larger stones are to be found on the top and off sides of the bank, and the smaller ones on the front slope and nearer the base on the sandy layer. This distribution may be supposed to be due to the difference of force exercised by the fresh impact of the surf going upwards, and its exhausted power when the water travels back, under the influence of gravity alone, when again the larger stones are left behind, and the smaller ones and sand are carried down the slope. The surf wave on the above idea is supposed to strike the bank perpendicularly in front, but should it move against it obliquely, either on one side or other of the perpendicular, then the pebbles will be driven obliquely up the bank towards the UPPER SURFACE OF PEBBLE Sagitta AO&BO of terminal arcs, & CO & Do of side arcs acbd original fragment ground down to ACBD SIDE ASPECT OF PEBBLE Sagitta A0& BO of terminal arcs & C0& Do of arcs of upper and under surfaces. acbd original fragment. III. ACTION OF SURF ON PEBBLE BEACH stones of porphyry and quartzite. This also may be inferred from |