VII. THE FULLER'S-EARTH IN THE SOUTH-WEST OF ENGLAND.

By RALPH TATE, Assoc. Lin. Soc., F.G.S., &c.

In the early part of this year my honoured correspondent, M. Terquem, of Metz, applied to me for information respecting our Fuller's-Earth, as he was desirous to know the relations subsisting between the formation as developed in the province of the Moselle and in England. The account given of the Fuller's-Earth in our geological manuals is very meagre, and could serve very little my friend's purpose; but fully aware that such description did not embrace all that is known respecting the formation in this country, I had compiled the summary that here follows: and in addition supplemented our knowledge of the fossiliferous contents of the terrain by the determination of a large suite of fossils in the collection of the Geological Society. These new materials render no longer tenable the inferences that have been drawn on the affinity of the fossils.

The geological reader is aware of the great lithological and in part palæontological differences which exist in the Lower Oolitic strata at the opposite extremities of their range in England. In the belief that the present communication, brief though it be, is the fullest exposition of the history of the Fuller's-Earth in the southwest of England, I trust it will prove of service in future attempts to correlate satisfactorily some one of the members of the Lower Oolite of Yorkshire with that of the typical Fuller's-Earth.

*

I may state in passing that the Fuller's-Earth in the department of the Moselle has yielded more than 300 species of fossils, not including microscopic forms, which number nearly one hundred; M. Terquem has divided the formation into three zones of life-the inferior characterized by Ammonites Niortensis; the median, by Ammonites Parkinsoni; and the superior, by Ammonites Backeriæ. No such divisions have been made out in the English beds.

Extent and Thickness of the Fuller's-Earth in the South-west of England. With the other members of the Lower Oolite, the Fuller'sEarth has more or less of uniformity as regards its constitution and fossil contents from Dorsetshire to the borders of Oxfordshire. Throughout this tract, it presents an argillaceous character with thin beds of limestone and calcareous nodules. The underlying formation is, in every instance, the Inferior Oolite; but from the Dorsetshire coast to near Hinton, on the borders of Somersetshire and Wiltshire, it is overlain by the uppermost members of the Lower Oolitic series, and to the north of that locality the Great Oolite appears, and throughout the further extension of the Fuller's-Earth is the overlying formation.

* In litteris.

At Bridport, on the coast of Dorsetshire, the Fuller's-Earth attains a thickness of 150 feet; and near Bath, where it forms a conspicuous band, it is 140 feet thick; at Wotton-under-Edge, 128 feet; near Stroud, 70 feet; and in the north of Gloucestershire, as near Cheltenham, it is further reduced to a general thickness of from thirty to forty feet. It appears at Sherborne, near Burford, to the northeast of Cheltenham, and does not extend as far east as Oxfordshire, beyond which the Stonesfield slate rests on the Inferior Oolite. The horizontal extension of the typical Fuller's-Earth in the southwest of England, which is about 180 miles, is very much the same as that of the Upper Lias Sands-preserving a maximum thickness from Bridport to Bath, but attenuating rapidly to the north and east, and finally thinning out a little to the north-east of Cheltenham.

Lithology.-The peculiar mineral from which the formation derived its appellation, is confined to particular districts, as around Bath and Stroud, and where it does occur, constitutes but a very small portion of the thickness of the formation. This Fuller's-Earth is used in fulling cloth. The lithological characters of the formation may be gathered from the following sections:

1. Cliff at Watton Hill, west of Bridport Harbour, "composed principally of blue clay, grey marl, and marlstone, with subordinate beds of imperfect stone; thickness of 150 feet; the base reposes on the Inferior Oolite, and the formation is covered by the ForestMarble."*

2. Bath, in descending order :

A. Blue and yellow clay, with nodules of indurated marl 30
B. Bad Fuller's-Earth

C. Good Fuller's-Earth

Feet.

40

3

5

2.5

D. Clay, containing beds of bad Fuller's-Earth and layers
of nodular limestone and indurated marl

100

135.5-148

Bed D encloses one or two strata of a tough, rubbly limestone, which is commonly called Fuller's-Earth rock, and bears considerable resemblance to Cornbrash. This rock is always accompanied by an immense number of Terebratulæ, and Mya angulifera and Isocardia concentrica are almost invariably found in it.t 3. Slaughterford, East Gloucestershire : ‡—

White marls, with occasional stonybands

White and grey limestone, and Fuller's-Earth rock
White and blue calcareous clays with Terebratulæ

Feet.

4. Near Cheltenham.-The deposit consists of regularly bedded blue and yellow shales, clays and marls, with occasional courses of

* De la Beche and Buckland, Trans. Geol. Soc.,' 2nd series, vol. iii. (1830). Lonsdale, Geol. of Bath, Trans. Geol. Soc.'

Hull, Mem. Geol. Surv., sheet 34.

rubbly limestone or calcareous sandstone. Most of the limestones are a lumachelle, some of them being entirely composed of Ostrea acuminata cemented together."

*

Paleontological Features of the Typical Fuller's-Earth.—The Fuller's-Earth does not possess a special fauna, and though regarded usually sterile as to the number of species, yet it is characterized by the profusion of Ostrea acuminata, Terebratula ornithocephala, and Rhynchonella varians. Professor Ramsay† summarizes the species of the Fuller's-Earth as follows:-Echinodermata 1, Conchifera 17, Brachiopoda 4. Total species 22, and remarks thereon:-"The majority of the forms that passed upwards from the Inferior Oolite limestone seem to have fled the muddy bottom of the Fuller's-Earth sea, and to have returned to the same area when the later period of the great oolite began The Fuller's-Earth may be considered only as a comparatively unfossiliferous and inconstant lower zone of the Great Oolite." The inference stated in the first sentence of the quotation is not consonant with facts; for in the first place that portion of the Inferior Oolite which has furnished the larger proportion of Great Oolite species, and indicates similar conditions of deposition, is that of lower freestone beds and pea grit of Cheltenham, which occupy the base of the Inferior Oolite, and in the second place, of the species common to the Inferior Oolite and Great Oolite, those which appear in the later stages of the former formation, occur also in the Fuller's-Earth. The second sentence of the above quotation is no longer applicable, inasmuch as though the fauna of the Fuller's-Earth is not exceedingly rich, yet far exceeds in number the then catalogued species, and, as I shall endeavour to show, has a greater affinity to the Inferior Oolite than to the Great Oolite.

The number of species catalogued by me from the Fuller's-Earth is 93, distributed in the following classes:

So that the Fuller's-Earth is not so barren in species as is generally supposed. Of the 93 recorded species, two, Montlivaltia tenuilamellosa and Belemnites parallelus, have not been found in any other formation; and respecting the range of Myacites Terquemus, Buv, and Pholadomya truncata, Buckman, I have no information; 6 forms are at present undetermined, whilst the bulk of the species, 81, occur in either the Inferior Oolite or Great Oolite, or in both formations.

* Hull, Mem. Geol. Surv., sheet 34, p. 11.

† Anniversary Address Geol. Soc., 1864.

See Lycett Cotteswold Club, vol. i., p. 71 et seq.; and Wright, Q. J. G. S., vol. xvi., p. 11.

The range of the 84 determined species is as follows:

Accordingly, 69 species, or 83 per cent., occur in the Inferior Oolite, and 49 only, or 60 per cent., are found in the Great Oolite or superior formations. These results lead us to the inevitable conclusion, that the Fuller's-Earth is a subordinate member to the Inferior Oolite rather than to the Great Oolite, as hitherto considered.

The Inferior Oolite presents in its organic remains at least a twofold aspect, and whilst the older fauna is to some extent repeated in the Great Oolite, the newer fauna lived on during the deposition of the Fuller's-Earth, but did not extend into the Great Oolite. Indeed, the majority of the species common to the Fuller'sEarth and the Inferior Oolite made their appearance in time in the upper zones of the Inferior Oolite; such are:-Serpula tetragona, Holectypus depressus, Hyboclypus gibberulus, Clypeus Plotti, C. Hugii, Echinobrissus clunicularis, Waldheimia ornithocephala, Terebratula perovalis, T. globata, Rhynchonella varians, R. spinosa, Cypricardia Bathonica, Ceromya Bajociana, C. striata, Goniomya angulifera, Isocardia nitida, Mytilus Sowerbyanus, Ostrea acuminata, Pleuromya æquata, Pholadomya Heraulti, Ammonites Parkinsoni, A. discus, &c., &c.

And so close is the affinity subsisting between the fauna of the zone of Ammonites Parkinsoni and the Fuller's-Earth, that massing the species of these two horizons, the contrast in their numerical relations to those of the lower zones of the Inferior Oolite is as great as that which they present to those of the Great Oolite.

In conclusion, the Fuller's-Earth is not a formation, but only the uppermost, or a fourth, zone of the Inferior Oolite. Here, there is a marked decadence of Inferior Oolite species, yet at the same time the facies is decidedly after that fauna.

NOTICES OF SCIENTIFIC WORKS.

WROUGHT-IRON BRIDGES AND ROOFS.*

Or all materials used in construction in these days of progress, there is none which plays so important a part in engineering and architectural art as iron. This material has become the only resource of the engineer for carrying out those large designs and projects which thirty years ago would have been considered chimerical. The attempt to cross the Menai and Conway Straits with bridges formed of wrought-iron plates was treated by mathematicians and engineers as they would have regarded a chapter in the ‘Arabian Nights;' and more than one eminent mathematician pronounced the attempt however ingenious the combinations might be in the shape of iron plates-as a wild and fabulous scheme. It was only those connected with the preliminary experiments-which led to the form and principle of construction-who could form a correct idea of the project and establish with certainty the principle on which those important structures were founded.

It must be admitted that the position of the load and the form of its distribution were not attended to with the same mathematical accuracy as at the present day; but the general dimensions, extent of span, and weight of load were carefully considered, in order to resist every possible strain and to render the structures secure. All this was done in the face of detractors, and the doubts and fears of men of science, and the results are the completion of the Britannia and Conway Tubular Bridges, as they now exist, as firm and secure as the first day they were opened for public traffic. It is true that tubular bridges, such as the Britannia and Conway, are of a more expensive type than those subsequently introduced; but although extended practice and the progress of science may have suggested improvements, it cannot be disputed that all subsequent constructions of this kind are founded on the same principles as those to which we may safely refer as the pioneers of all their successors. We have a much greater variety in the forms of wrought-iron bridges now than when first introduced; but the principle, so clearly exemplified in the Britannia and Conway Tubular Bridges, is identical with more recent constructions in the balance of the two resisting forces of tension and compression, as exhibited in the upper and lower sides or flanges of those important structures.

*Wrought-iron Bridges and Roofs:' Lectures delivered at the Royal Engineer Establishment, Chatham. By W. Cawthorne Unwin, B.Sc. Associate Inst. C.E. E. & F. N. Spon.