tendence of Mr. Michelmore, of Berry, Totnes, was commenced in 1860 and finished in 1873. Total length 1823 feet, average height 16 feet, average thickness at foundation 6 feet." It was so placed that the grass-grown summit-levels of the old beach lay behind it, while for about 700 feet at the eastern end it fronts and protects the cliff; here, of course, it was built at the shoreward limit of the beach. The foundation is for the more part on the materials of the submerged forest beds, and hence an exposure of these by the occasional fall of the beach has usually been followed by considerable damage to the wall. If the foundation is at times exposed, on the other hand the sand and shingle sometimes rise to within one foot of the top of the wall, but never throughout its whole length at once. They stood at this height when I visited the spot on the 14th August, 1908. It follows that against the wall there is from time to time a variation of at least fifteen to sixteen feet in the level of the beach. On the same date I observed the gradients of the beach. At high-water mark of that day the gradient was 1 in 41, and this passed through a decreasing range to a fall of 1 in 6 at low-water mark. Above high water, and separated from it by a narrow level surface, was an old fall of the beach, which had a gradient of 1 in 2ğ, probably the steepest at which this sand and shingle would naturally dispose itself. On the whole the material is distinctly smaller in size than at Hallsands, but I have not estimated the proportion of finer and coarser on this beach, or taken any measures for accurately comparing it with the Hallsands shingle. Much fine gravel is, however, to be found on the foreshore at Blackpool of a grade which is practically confined to parts below low water at Hallsands. The fine gravel I have graded through sieves with round holes, with the following result, the percentages being expressed by weight. This is by no means a fine sand, the smallest particles, under 1 mm., are almost entirely small chips of the local slate, chips of flint, and fragments of shell. The fine gravel, of which the mechanical constitution is given above, was also examined lithologically. For this purpose it was divided into two parts, the particles which were left on the sieve having round holes of an inch in diameter, and the particles which passed through such sieve. The analyses expressed as original rocks are as follows, percentages being expressed by weight :— Analysis A. Particles over 20 inch. per cent. Quartz Flint Devonian Dartmoor Organic 23.4 9.4 12.1 0.5 100.0 In each analysis it was found practically impossible, except with undue labour, to ascertain precisely how much of the quartz sand was of local origin, and how much came from Dartmoor, but a fair proportion has obviously been derived from the latter source. Materials definitely classed as " Dartmoor" are all either felsites or quartzschorl rocks of highly distinctive character. 66 Devonian" comprises small tabular fragments of the local slates, and a much less proportion of particles of local igneous rock, conveniently termed "diabase." Something more than half the fine material is certainly foreign to the locality. Two hundred and fifty pebbles taken from the beach were also examined; these were not picked up by myself, and accordingly any unconscious geological choice was avoided. In size they ranged from about 11 inches to about 4 inches in greatest diameter, the majority measuring between 21 and 2 inches. This collection also was analysed lithologically. Analysis C. Pebbles of from 1 to 4 inches greater diameter. Devonian fissile slates, soft and in thin flat stones Vein-quartz from the Devonian slates Devonian igneous (diabase) Quartzites, foreign to the locality Flint Dartmoor Rocks This analysis gives 47.2 per cent of rocks derivable from the adjacent cliffs, and 52.8 per cent foreign material. But in reality the proportion of local rocks, effective as beach-forming material, is considerably less, since the Devonian slates are mere temporary constituents, liable to total destruction after a brief succession of stormy days. The average weight of the pebbles included in this collection of 250 was 1.95 ounces, and the quartzites were the largest, averaging 3·14 ounces, although much more thoroughly rounded than the vein-quartz pebbles, which averaged only 1.95 ounces. The average of the flints was 1.64 ounces. While at Hallsands there is little cliff capable of yielding much material for beach formation, at Blackpool the cliffs are not only of a different and more easily broken rock, but have long been much more fully exposed to the waves. None the less, in all the time which has elapsed since the forest was submerged, they have not been able to supply sufficient material, by way of replacement of wear and tear, to constitute one-half the total beach. Wear and tear, as aforesaid, has so far reduced the beach that it is not now, and has not for at least a hundred years past, been sufficient to ensure that the substratum on which it rests shall be protected from marine erosion. From time to time the clays and peat of the submerged forest are exposed, and each time some small part is removed, lowering the foundation of the beach. Here too, as at Hallsands, the adjacent sea-bed is no possible recruiting ground for a shingle beach. At Hallsands and at Blackpool I have now had reason to thoroughly examine the beaches; Slapton Sands I have somewhat more casually examined, but find them more closely resembling the first-named. The evidence is abundant and clear that the whole of Start Bay is fronted with shingle of foreign origin, and that any loss to its total quantity is permanent. It is also clear that a flint and felsite beach, once its constituents are well water-worn and rounded, is a singularly permanent institution. But Blackpool proves that it does in fact wear out by natural agencies, aided by occasional human interference, and must, sooner or later, become an inadequate protection to the coast, and Hallsands proves that any artificial abstraction in this way is a permanent loss. Notwithstanding which determined facts, the beach material at Slapton is still for sale, and may be purchased in cartloads from the local Rural District Council. Is it too much to hope that wiser counsels may yet prevail, and slight present convenience be sacrificed to avoid future permanent loss? Once let the beach at Slapton cease to be an adequate protection to the coast, and a main road as well as very many acres of arable land will be destroyed by the sea, while Slapton Lea will cease to exist. A beginning has been made in a correct policy in closing Blackpool to all shingle seekers, and the extension of this closure to the whole bay would be a wise step, necessary to the protection of the land. A Royal Commission is sitting which is 'inquiring into the defence of the shore from erosion, and at the same time no one moves to ensure that Nature's provision for the protection of our Devon coast be maintained. ON A FURTHER DISCOVERY OF FOSSIL FISH AND MOLLUSCA IN THE UPPER CULM MEASURES OF NORTH DEVON. BY INKERMANN ROGERS. (Read at Launceston, 29th July, 1909.) 66 THE results of recent geological work in North Devon certainly illustrate the truth of a remark made by Gilbert White: That district produces the greatest variety which is most examined." There was a time when the Upper Culm Measures of North Devon, with the one exception of the small group of rocks associated with the Culm beds in the Bideford district, were regarded as so barren as to be hardly worth searching for fossils. Sixty years ago, for instance, in his Chapters on Fossil Botany, Mr. S. R. Pattison1 mentioned as a "phenomenon in this uninteresting district" the "frequent occurrence and enormous extent of sheets of sedimentary matter entirely destitute of organic forms." This opinion regarding the Upper Culm Measures has also been shared by nearly all geologists until quite recent times, and an unfavourable view of the opportunities which the neighbourhood presents for field work could not fail to be strengthened by the crushed, contorted, and folded condition of the strata, and also by the fact that many of the sections occurring in the cliffs are inaccessible except to skilful and experienced climbers. Yet that in reality the district is very far indeed from being uninteresting to the geologist, has, I hope, been placed beyond all doubt by the various papers dealing with the subject which have been published since 1904.2 These records show that not only have fossil plants been found here and there throughout the Upper 1 Pattison (1849), p. 161. Full reference will be found in the Bibliography at the end of this paper. 2 Arber (1904), (1905), (1907). Rogers and Arber (1904). Rogers (1907). |