Excursion to Bridport, Bothenhampton, Burton

200 SECOND DAY.-EXCURSION TO BRIDPORT, BOTHEN HAMPTON, BURTON BRADSTOCK, BRIDPORT HARBOUR, AND EYPE. (Report by HORACE B. WOODWARD.*) On Tuesday morning the party started a little before ten o'clock from the Bull Hotel at Bridport, after being joined by a small detachment of Members who came from Yeovil by an early train. The weather was dun and misty, so that Colmer's Hill, a conical knoll 370 feet high, formed of Inferior Oolite Sand, and usually a conspicuous feature in the landscape west of Bridport, was only just visible as the members passed the Market House. Proceeding along South Street towards Bothenhampton, the evidences of terrace-cultivation were noticed on the hills east of Bridport. Here in some cases narrow strips of cultivated land, still enclosed by hedgerows, fringe the higher slopes of the hills, ranging one above the other, and varying in length, breadth, and inclination. Rarely the strips stretch across the hills, as indicated by hedge rows still remaining near Walditch i but in other cases, where no hedgerows exist and the land has been turned into permanent pasture, the slopes present the remarkable features called " linchets " or ,. balks," which are simply the banks or ridges which formerly divided the strips of cultivated land. They are of some geological interest, as they occasionally exhibit a resemblance to parallel terraces, and they have actually been described as raised beaches! t Such terraces are of frequent occurrence along the Dorset coast, in the Isle of Purbeck, and near Abbotsbury, as well as near Bridport and on the slopes south of Burton Bradstock: many, too, have been noticed in other locali ties. While in some cases such appearances may be caused by Iandslips, yet there is little doubt that the majority of these terraces were, as pointed out by Mr. G. Poulett Scrope, "worn by the plough at a time when these slopes were, if they are not still, under arable cultivation." For he remarked that the " down-hill tendency of the disturbed soil is greatly assisted by the wash of II Much of the information here given has been collected during a re cent examination of the district for the Geological Survey. It is here prmtod, in advance of the official publication, by permission of the Director-General.-H. B. W. t See D. Mackintosh, • Geol. Mag.,' Vol. iii, pp. 69, 155; and' Scenery of England and Wales,' 1869, p. 84. EXCURSION TO BRiDPORT, BOTHENHAMPTON, ETC. 201 heavy rains upon the sloping surface, and the result is that, year by year, the whole surface-soil of the slope, when und er continuous arable culture, is slowly, indeed, but surely, travelling downwards until it is stopped by some hedg e, or wall, or bank, which limits in a downward direction th e disturbing action of the plou gh." '* The writer remarked that on th e I sle of P ortland, where freehold land ba s been divided and subdivided, narrow strips of land arc ofton cultivated j and , near the high er lighthouse, lie had noticed in a breadth of about a quarter of a mile no less than 35 strips of land on which crops of corn, grass, and potatoes were alternately grown. In such a tract, when arable cultivation is succeeded by pasture, no doubt It series of ridg es or " terraces " will mark the change that has taken place. Passing through Bothenhampton, the Members proceeded to the quarries in the Forest Marble, situated to the south of the village. Here this formation is seen dipping to the northwards, towards the Middle Lias, against which it is faulted. The fault is no doubt a continuation of the disturbance (to be mentioned further on) which brings the same formations in abrupt contact to the east of Eype's Mouth, where the downth row must be at least 425 feet. The hill side south of Bothcnhampton is scarred with old pits from wh ich the Forest Marble bas been raised for many years past, the stone having been worked on a dip-slope. Here three main divi sions in the formation ar e to be observed- an upper division of shales and shaly limest one, with thin beds of shelly limest one ; a middle division of shell-limestone (about 12 feet of which was expose d) ; and a lower divisi on of shales and thin lim estones. The junction with the basement beds of the Oornbrash may be seen in a lan e-cutting south of Bothenbampton church, where grey sandy lim est ones and marls, with Aviwla ecliinata and many brachiopods, rest on flaggy shell-limestones and clays that form the upper part of th e Forest Marble. Th e main mass of stone for which the Bothenhampton quarries have been opened is a blui sh-colour ed oolitic and sh elly lim estone, very much false-bedded. This rock, known as " B'ampton Stone:' is used for building purposes, and for road-mending, and sla bs are obtained for piggeries and for stiles. It is too much impregnated with ochreous galls to be useful as marble. Prof. A. H. Church II 'Geol. Mag.,' Vol. iii, p. 293. 202 E XOURSION TO BR ID POR T, nO THENHAUP TON, ETO . is of opinion that iron-pyrites has originally been th e colouring material of the blue bands of the Forest Marble, and that the yellowish-brown exterior is dne to the oxidation of the pyrites.* Among the fossils to be observed in the ston e arc Pecten lens, P. vagans, Lima duplicata, L. cardiiformis, Ostrea Soioerbui, Cyprilla L oweana, and Apiocrinus P ark insoni,t J oints of th e last-named fossil, termed " Coach-wheels," are not uncommon. Some reptilian bones have also been obtained, as well as fragments of lignite. Curious markin gs are abundant on some of the sur faces of th e sandy limestone-shales, and th ey appear to be tracks of invert ebrate animals. It was pointed ont that the Great Oolite developed near Bath and for some distance to the south of that city does not occur so far south as Dorsetshire, being represented perhaps in part by th e Forest Marble, and in part by the Fuller's Earth. Pa ssing up a narrow and somewhat dirty lane, th e Members now ascended by some old quarri es to th e top of the hill. Here a splendid view of the country was unfortunately eclipsed by the mist. The scenery is indeed diversified, and in clear weathe r th ere appears at first to be little system in the arran gement of hill and vale. 'l'his is in part dne to th e overlap of the Chalk and Uppe r Gr eensand over the Jurassic rocks, the newer strata resting on different members of the latter series j and the irregul arity in the features is also in part due to the faults which here and there have displaced the Lia ssic and Oolitic rocks. Apart from th e general influence of stratigraphi cal arrangement, the influence of lithologi cal characters is likewise mark ed. The Greensand, as u rule. stands out boldly, forming the gorse-clad hills of Eype Down and Ship ton Beacon, and, further off, th e" Alps of Dorset," or P illesdon P en and Lewston HilI , known to sailors as the" Cow and Calf." The flat-topped hills, capped by In ferior Oolite, are readily distin guished from th e grassy knoll s formed of the Oolite Sands ; while th e well-cultivated tracts of the Middle Lias, marked by small enclosures and famed for orchards, appear in contrast with th e wet and less productive t racts of Fuller's Earth or F orest Marble. * 'Quart. Journ. Chem, Boc.,' Seri es 2, Vol. ii, p, 379. t The fossils menti oned in this paper, except where otherwise stated, were identified by :Messrs. G. Sharman and E.T. Newto n. See also Wrigbt, • Qnar t. J ourn. Geo1. Soo.,' Vol . xii, p. 310; and Damon, • Geology of Wey. month, ' &0" 1884, p. 223. ltXCURRION TO BRIDPORT, ROTHENHA!>!PTON, ETC. 203 About half a mile west of Burton Bradstock a small quarry in the Inferior Oolite was visit ed. Th e bed s here work ed belong alui ost entirely to th e zone of Ammonites Parkinsoni, represented by pal e gl'pY oolitic and sandy lim estones, below which n bell occnrs in which Bra chiopoda ar e as abundant (s o one Memb er ob served) as " plums ough t to be, in a pudding." Ter ebratula splus roidalis is the comm on form. Other fossil s met with in th ese beds ar e RJ,yn chonel/a spinosa, Terebratula Phillipsii, 1'. glubata, and Waldheimia carinata. *' Echinoderms, represented by Oolinrite» rinqens and .lIolecl!J[llis tiemisplue ricus, are not uncommon. Ammo nites Humpliriesianus occur s in th e Terebratula bed, and als o in the iron-shot limestone exp osed at th e base of the quarry. To the south of this pit, on the northern slope of the hills stretching towards Bridport Harbour, are several old pits, exca vated for the most part in the brown, and sometimes blue, iron shot limestone which forms th e lower portion of the Inferior Oolite of this district. He re the stone has been largely us ed for building the wails which divide th e fields. In these beds Ammo nites Mur chisonai has been found, and Waldheimia carinata is 11180 more abundant than in the upper strata. Th e Memb ers now descended the hill, and taking a footpath through th e meadows, crossed the little River Bredy, and p ro ceeded to the deep road-cutting south of Burton Bradstock.

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