Further Observations on the Geology of Ridgway near Weymouth
Authors: Weston Charles H. 
Published: October 2009

In his former paper on this subject* Mr. Weston endeavoured to show the existence of the Hastings sand at Ridgway. He has since visited the various sections of the Wealden between Hastings and Lulworth, and then re-examined the railway cutting at Ridgway, and the result has been to confirm his former views. He finds that the variegated clays, loams and sands exhibited in the latter locality are by no means local, but occur also in Kent, in the south of Sussex, in the Isle of Wight and in Dorset; and he has recently observed them on the Brighton and London Railway near Balcombe. In Sussex these variegated clays form a very subordinate part of the formation, but are more developed in the counties to the west.

In his concise but masterly ‘Geological Sketch of the Vicinity of Hastings,’ Dr. Fitton notices the “greenish and purplish variegated clay” and sand visible at Leaness Point, between Hastings and Winchelsea. They lie beneath a stratum which Mr. Webster describes as a sandstone intersected by numerous veins of argillaceous iron ore, and rest on a dark-coloured shale also containing several layers of rich iron ore, formerly much worked in Sussex. These lowest shales are placed by Dr. Mantell in the upper part of the Ashburnham beds. Dr. Fitton also points out the anticlinal axis passing from the shore near Leaness through the highest point of Fairlight Down to Battle, the strata dipping away from it on both sides.

Mr. Weston has himself found similar ferruginous and variegated clays and sands in a hill beyond Ham Street on the Rye and Ashford Railway, and near Hastings at Bopeep, west of St. Leonard's, and at Bexhill. He next found them at Sandown Bay in the Isle of Wight, and also between Atherfield and Afton Downs. The clays contain no fossils but the
Cypris valdensis
and
Paludina
in some associated beds.

“The next appearance of the Hastings sand is at Swanage Bay in Dorset, emerging from under the very steep escarpment of Ballard Downs. The entire group was in this place more varied, and consisted of a greater number of alternations of sands and clays than I found in the Isle of Wight. It appeared in consequence to combine in miniature the more extensively-developed arenaceous deposits of Hastings and the almost exclusive argillaceous strata of the southwest coast of the Isle of Wight.

“The variegated clays are indentical with those of the latter and of Ridgway. I could however discover no fossils in them.

“The Chalk Downs (of which Ballard Down forms the southeastern extremity) run across the Isle of Purbeck and terminate in the fine bluff cliff of Purbeck Hill on the east of Lulworth. The sections below Purbeck Hill are those of Worbarrow Bay on the east of the chalk and Mewp Bay on the west, of which I only visited the former.

“The Hastings sands of Worbarrow Bay consist of a considerable admixture of clays and sandstones. The latter appear to abound here more than at Swanage Bay. The clays posses the peculiar character and colours of those at Ridgway, but some of their colours are rather more vivid. The colour of the sandstones, from the great abudance of the ferruginous base, is in many places intense. I could not discover any organized remains in these clays. I think no one who has examined this part of Dorset, and has traced the base of the chalk escarpment from Ballard Down to Purbeck Hill, can fail to be convinced of the correctness of Dr. Fitton's view, and to feel satisfied of the continuity of the Wealden formation right across the peninsula of Purbeck.”

He next visited Lulworth Cove, where the general appearance of the Hastings sand is similar to the localities we hav already described. Not far from this place is the last coast exhibition of the Wealden formation in Man-of-War and Durdle Coves. These are separated from each other by a short isthmus, which has been protected by a rock of greatly-inclined strata of Purbeck stone, and is composed of the Wealden very condensely and vertically developed. From this isthmus we see the eastern side of Man-of-War Cove, which appeared evidently to consist of Hastings sand. That point and the isthmus are clearly the remnants of a once continuous mass. The west side of Durdle Cove is composed of chalk which here abuts upon the sea, and runs uninterruptedly along the coast to the high point of White Nore, whence it trends inland.

In all these sections the variegated clays, loams and sands were identical in character with the Ridgway deposit. In this section, which he visited the following day, Mr. Weston “traced the Purbeck beds to their first uninterrupted termination, which consisted of calc grit with Purbeck fossils. Beyond this were clays, and then alternations of the calc grit and clays, and ultimately the Hastings bed exclusively. This section therefore exhibits the same features which Dr. Fitton has observed respecting other sections of the Wealden, showing, 1st, the continuity and sequence in the deposition; and 2ndly, the quiet process of such deposition. Hence we have the most satisfactory evidence that the beds overlying the Purbeck followed in regular succession, and were in fact rather a continuation of them.”

On the whole Mr. Weston concludes not only that the variegated clays of Ridgway Hill really belong to the Hastings sand formation, but that their geognostic position is in the lowest part of the Worth and Tilgate group, separating it from the inferior Ashburnham beds.

Mr. Weston also mentions that he found the Purbeck deposits to extend as far west as the end of the Corton Range, and therefore spreading co-extensively with the Portland oolite to the vicinity of Portisham.

In regard to the attempt to explain the singular interposition of the Oxford clay between the Wealden and the cretaceous series as resulting from a drift, he remarks:—

“1st. That I could not perceive in the fossils those marks of abrasion which would indicate their having been drifted.

“2ndly. That the Oxford clay has considerable depth. It has already been penetrated to the depth of about sixty feet without reaching its termination.

“3rdly. That the vertical surface of the wall of chalk is hardly consistent with the natural results of previous diluvial action in that locality. And,

—4thly. In many places the theory of a drift may involve no physical difficulties. But at Ridgway this idea would involve serious objections. Whence, it might be asked, could the Oxford clay have been drifted? The Oxford clay of Ridgway is about 200 feet above that of Weymouth; and the next exhibition of that bed on a higher level would be at Little Bredy near Abbotsbury Common, at a distance of between five and six miles, and at a level, I apprehend, certainly far below that of Ridgway. Whatever difficulties may therefore be supposed to attach to the theory which I have ventured to propose, will not, I think, be diminished by the suggested explication of a drift. I have also satisfied myself by repeated and careful examination that the section contains no double fault.”