85

CHAPTER VII

Phaneritic series-Raised Beaches-Sea Margins. Ayres. Caves-Sand-drift -Muirband or Pan-Lake Deposits.

THE group of strata now remaining to be considered, presents characters so easily observed, that one may well be surprised that any difficulty should have occurred, either in the description or explanation. A few only of the series present themselves to our notice in this district, of which the first is the most interesting.

1. Raised Beaches.-It has been announced by nearly all our local geologists, that there is a belt of level land around the coast, and raised several feet above the grass line or ordinary high-water mark, containing, along with sand and gravel, numerous remains of marine shells. It is also announced that the level land terminates inland, at a greater or less distance from the present beach, immediately at the base of a cliff or terrace which had occupied the position of a sea-margin; and that the rocky cliffs contain caves, the mouths of which are at a considerable elevation. It has been assumed, in order to account for this level belt and these caves, that the sea formerly occupied the place of an ordinary beach between high and low water, but that, in consequence of an upheaval of the land, this beach now appears at a higher level, and may be regarded as a proof of an elevating process. Instead of adopting such hypothetical notions, which unfortunately have passed current in this quarter for the last score of years, and have been earnestly advocated by such observers as Maclaren, Milne Home, and Hugh Miller, in which considerable liberties have been taken with molluscan life, on, apparently, very slender acquaintance, we shall venture to discuss the subject and examine the proof adduced.

Meanwhile, it may be stated that there is required for the examination of this deposit of marine matter, above the present sea level, an acquaintance with the habits of the animals, the relics of which are appealed to as furnishing the requisite evidence, with the mode of distribution of the materials of a beach, and with their relation to the shell-fish attached to them, together with the peculiar oscillations of the sea in its statical and dynamical condition. That these requisites have not been possessed by all our speculators will very easily be made manifest.

Mr Cunningham is perhaps the only local observer who seems to hesitate respecting this generally received notion of upheaval, for he says, "That some of these deposits of existing shells are in situations relative to the sea, which its present level and other circumstances seem inadequte to place them in, we may at once affirm; but there certainly seems to be no reason why such appearances should be referred to a rising of the land, rather than to a local recession of the sea, and, if we consider the esturial character of the firth, perhaps the latter may be most likely." (Geol. of the Lothians, p. 117.) As the peculiar changes, by which the surface of the sea in the Forth might be permanently depressed, have not been mentioned, we are not in possession of the means by which to judge as to the probability of such an event, and, we may add, that the internal character of this belt of land furnishes proof, as we shall presently point out, that such an explanation is unsatisfactory.

Mr Milne Home, in his valuable Memoir, to which we have so frequently referred, seems to have adopted the upheaval notion without reserve. In reference to this deposit, at Skateraw, near Dunbar, he states, that it " contains numerous fragments of limestone, derived most probably from the strata of limestone which occur in the immediate vicinity, to the north and west. Most of these limestone fragments are bored with Pholada, and I found the shell in the stone. Moreover, some of these fragments had smooth surfaces, and on some of them I found numerous specimens of Serpula and Patella vulgaris sticking. These shells are now, therefore, in the exact situa

tion where they lived.

At this place the shelly deposit is thirteen feet above high-water mark," p. 70.

The occurrence of blocks of limestone, whether at thirteen or thirty feet above high-water mark, perforated by Pholado, and the shells sticking in the holes, is no proof that these remains are in the exact position in which they lived, unless in reference to the block of stone. If Mr Milne Home had stated, that in all the blocks the holes with the shells were placed perpendicular to the horizon, the upright position being the natural one, his proof that the blocks had not been tossed about but simply elevated, would have been deserving of attention. But not aware of this feature of pholadean life, very different from the irregular boring propensities of the Saxicava arctica, he jumped to the conclusion, that blocks perforated by a pholas must have been covered at the time of the excavation by the tide, and since elevated, but preserving their natural position. We can supply this defective observation, having visited the spot, and can assure the reader, that the direction of the holes has no uniformity, but, on the contrary, furnishes satisfactory proof that the blocks had been lifted from their bed and irregularly distributed on the banks. The serpulæ, being cemented to the rocks, could not readily be displaced, and the limpets, still found adhering, had been prevented from crawling or falling off, by the mass of sand and gravel in which they were imbedded. They died on the spot, but their death was a violent one.

The same author records, as another example of upheavel, a mass of sea-shells sixty-two feet above high-water mark, half a mile to the east of St Colme Lodge, between Aberdour and Dalgetty Church. He says, "I found in the cleft of a sandstone rock a confused heap of oysters, limpets, and whelks." (Parallel Roads of Lochaber, p. 28.) This mass occurs towards the top of a wooded bank immediately eastward of the Lodge, and about a mile to the westward of Aberdour. On visiting the spot shortly after the discovery was announced, there did not appear the slightest trace of sea-sand or gravel. The shells were all of the edible kinds, and were imbedded in a brownish clay soil, in

which I observed fragments of splint coal and a coal-cinder. Recently I had an opportunity of looking at them, and observed at one place two limpets, one within the other, and in another place a string of four similarly inserted. Weak must be the evidence in favour of upheaval, if such an example be regarded as yielding any support.

Mr M. Home has likewise stated, that "at Joppa, and at a height of from two and a half to three feet above high-water mark, a stratum of fire-clay, which was excavated for working two years ago, was found extensively perforated by Pholas crispata, which exists now in the Firth, but is never known to live higher than half tide. The borings indicate, therefore, a change of level to the extent of nine or ten feet at least." (Ib. p. 26). This excavation has been obliterated, so that no satisfactory examination of appearances can be executed at present.

Mr Maclaren, in his Geology of Fife and the Lothians, p. 228, adopts, in like manner, the notion of upheaval, and states unreservedly that "there is satisfactory evidence to prove, that the bed of the Firth of Forth, and the land on both sides of it, have been raised twenty feet or more, at an epoch which, though very recent, geologically speaking, is probably long anterior to the records of history." The proofs adduced in support of this opinion are nearly similar to those already noticed, and liable to the same objections. He says, "The stratum of gravel in which the shells were chiefly found was from six to eight feet above the highest spring-tides, and about twenty-six or twenty-eight feet above the lowest level of low-water. Now, oyster-beds are found at all depths to 100 feet, but never, I believe, in spots left dry by the ebb-tide. The oyster-shells in the gravel were, therefore, about thirty feet above the level where the fish now lives; and the same remark applies to most of the shells found along with them; while the mussel, which is absent from the deposit, has its abode between high and low water."

There is here an appeal to molluscan life which merits consideration. That species of the genus OSTREA may be found at the depth of 100 feet will readily be admitted; but where

is the proof that the common oyster (OSTREA edulis), the species under consideration, ever lives at so great a depth? On our coasts it is dredged in five or six fathoms, and in some places occupies such shallow ground as to be fished up with a rake. In reference to the wader, termed HEMATOPUS ostralegus, Brisson, in his Ornithologie, says, "On le trouve sur le bord de la mer, où il mange beaucoup d'Huitres; ce qui lui a fait donner le nom d'Huitrier," v. 42. Pennant, in the well-known work BRITISH ZOOLOGY, is more explicit, for he says, "On the coast of France, when the tides recede so far as to leave the beds of oysters bare, these birds feed on them, forcing the shells open with their bills," Vol. ii. p. 482. But even admitting the depth of water in which oysters live, their appearance in this deposit has no resemblance to their arrangement in their natural bed. They are distributed among the sand and gravel in such a manner as to indicate that they have been borne from their residence and assorted by moving water.

This author has more recently furnished what he considers undoubted proof of the upheaval of the land, as indicated by a bed of cockles which he has examined at Bo'ness, and which we shall give in his own words,-" This deposit of shells is situated about a mile and a half west from Borrowstounness, where the Carse of Falkirk terminates in a strip of flat land a furlong in breadth. The shells are exposed in two openings, each about 300 feet long, made in the soil to procure limestone for Mr Wilson's ironworks. The bed can be traced in these openings along lines having an aggregate length of 1000 feet. Over all that space the shells form an unbroken stratum of very uniform depth (nearly three inches), and almost perfectly horizontal. They are covered by a bed of dark-brown sandy clay, from two to three feet thick, and rest on a deposit of the same substance, which closely resembles the mud spread over the present beach. The shells are all of one species, the cockle, or Cardium edule, and of various sizes down to the most minute. They are mixed with a portion of the clay which covers them, but lie so compactly, that they present to the eye the appearance of a layer of chalk nodules. Very few of