sections of passage-beds belonging to this subzone are to be found in that district. The most extensive exposures are those afforded by the cuttings on the Ashbourne & Buxton branch of the London & North-Western Railway, between Tissington and Alsop-en-leDale Stations. The geology of these cuttings has been admirably described by Mr. H. H. Arnold-Bemrose, in whose papers' detailed measurements of all the sections will be found.

(i) Sections on the railway between Tissington and Alsopen-le-Dale.

(a) Tissington cutting."

In this section, a series of alternating limestones and shales, about 100 feet thick, overlies the bedded tuff; but the true Pendleside Shales are not reached. Both lithologically and palæontologically this series constitutes a splendid development. of passage-beds. Thin bands of limestone, often argillaceous, and generally cherty, alternate with thick and thin beds of black shale; and massive beds of shelly, crinoidal limestone are occasionally intercalated. The limestones in this series contain an abundant and typical D, fauna of corals and brachiopods; while the shales contain lamellibranchs, including Pterinopecten papyraceus, Posidonomya Becheri, and Posidoniella lavis. A bed of black shale, only a few feet above the base of the series, contains Pterinopecten papyraceus in abundance.

(b) Highway-Close Barn cutting and Crake-Low cutting.

3

The sections in Highway-Close Barn cutting and in the northern part of Crake-Low cutting show parts of the series exposed in Tissington cutting. A comparison of these two sections illustrates the rapid variation in the development of shale at this horizon. In Crake-Low cutting the series overlying the tuff contains no appreciable amount of shale, but in Highway-Close Barn cutting, nearer Tissington, black shales are strongly developed at the same level.

(c) Newton-Grange cutting.

In Newton-Grange cutting the section exposes an anticline, and a comparison of the succession in the eastern and western limbs of Geology of the Ashbourne & Buxton Branch of the London & NorthWestern Railway: Part I. Ashbourne to Crake Low' Quart. Journ. Geol. Soc. vol. lv (1899) p. 224; and Part II. Crake Low to Parsley Hay' ibid. vol. lix (1903) p. 337. In the present partly-overgrown state of the embankments, the structure of some sections, where the beds are greatly contorted, is by no means easy to interpret; and I have found the descriptions given in these papers to be of great assistance in my investigations.

H. H. Arnold-Bemrose, Quart. Journ. Geol. Soc. vol. lv (1899) pp. 226-29 & pls. xvii-xviii. This section was independently described by Dr. Wheelton Hind, Trans. North Staffs. Field Club, vol. xxxii (1897-98) pp. Ĭ14-16 & pl.

3 H. H. Arnold-Bemrose, Quart. Journ. Geol. Soc. vol. Iv (1899) pp. 229-30 & pls, xvii- xviii.

the fold respectively brings out features of considerable interest. Detailed measurements of the beds in both limbs of the anticline have been recorded by Mr. H. H. Arnold-Bemrose, from whose description the thicknesses given in the following account have been taken.

1

In the eastern limb of the fold the descending sequence is as follows:

(4) Shales and thin limestones
(3) Tuff

(2) Shales and thin limestones

Thickness in feet. about 17

6

26

(1) Thinly-bedded limestones, compact in texture, with
chert; shale-partings in the upper portion about 100

That part of the section which comprised (2), (3), & (4) is now overgrown, but the whole series of cherty limestones (1) is excellently displayed. As a whole, the cherty-limestone series is poorly fossiliferous; but certain beds contain fossils commonly, and yield corals and brachiopods characteristic of D.

The fold is clearly dissected, and individual beds may be traced from one limb to another. In the western limb the descending sequence is as follows:

Thickness in feet.

(2) Grey, crinoidal, limestones without chert: to top of

section

(1) Thinly-bedded, compact limestones with chert

47

60

The crinoidal limestones (2) clearly represent the upper portion of the cherty limestones of the eastern limb. They are highly crinoidal throughout most of their thickness, and contain brachiopods

W.

Fig. 4.-Diagrammatic section of Newton-Grange cutting.

E.

b

a=Compact limestone, with chert and shaly partings. b=Crinoidal limestone, without chert. (= Black shale.

[Length of section=about 200 yards.]

in great abundance. In the lower part they have a conspicuous, wedge-like bedding, the beds thickening west wards. At the top of the cutting the gradual change from blue, compact, unfossiliferous limestone with chert into light-grey, highly-crinoidal limestone without chert, may be seen to occur within individual beds as these are followed from east to west. This change of lithological

1 Quart. Journ. Geol. Soc. vol. lix (1903) p. 339.

character, with a very localized development of highly-fossiliferous deposits, on a given horizon, constitutes a remarkable feature. Fig. 4 (p. 60) illustrates the section just described.

If the tuff occurring in this section is an attenuated portion of the thick tuff seen in Tissington cutting, the Cyatha.conia-subzone attains, in this neighbourhood, a thickness of well over 200 feet. About 100 feet of the subzone are represented above the tuff in Tissington cutting, while a thickness of about 125 feet is seen underneath the tuff in Newton-Grange cutting.

(ii) Bradbourne.

In the Bradbourne inlier, immediately south of the main mass of limestone and 2 miles east of Tissington, numerous small exposures indicate a considerable development of D,, with an abundant fauna. A quarry north of Bank House, at the eastern end of Bradbourne village, shows a good section of the thin limestones, with shalepartings, included in the subzone.

(C) Sections in the South-Western Part of the Area.

(i) Waterhouses.

In the extreme south-west of the area, exposures showing a highly-fossiliferous development of D, are afforded by two small quarries in the fields north of Waterhouses. These quarries lie respectively north-east and north-west of Field House. The beds consist of limestones with occasional shale-bands, chert being developed in the limestones.

(ii) Warslow.

On the western margin of the area, about 5 miles north of Waterhouses, three adjacent quarries lying to the east of the village of Warslow afford an extensive exposure of the upper part of the Carboniferous Limestone. The vertical extent of this section is over 300 feet, and the greater part, at least, must be assigned to the Cyathaxonia-subzone, but an upward sequence into the Pendle- * side Series is not seen. The beds exposed consist mainly of dark, thinly-bedded, cherty limestones.

Farther east, in the Manifold Valley, near Hulme End, cuttings on the light railway expose a series of thinly-bedded, cherty limestones with interbedded shales, belonging to D. The beds are considerably folded, and no great vertical thickness is seen.

(iii) Manor Farm, near Wetton.

East of the Manifold Valley, about 1 miles south-east of Warslow, and nearly 1 mile north of Wetton, a very interesting little section shows the uppermost beds of the Carboniferous Limestone and the lowest beds of the Pendleside Series in conformable

sequence. The section lies beside a stream, in a field immediately east of Manor Farm. The exposures are separated by gaps, but the beds throughout the section maintain a nearly-uniform dip, and there seems to be no doubt as to the undisturbed nature of the sequence.

The lowest beds of the Pendleside Series consist of hard black limestones, with interbedded black shales containing hard calcareous bands. Fossils, which are fairly common, include Posidonomya Becheri, Posidoniella minor, P. lavis, Aviculopecten Losseni, Glyphioceras striatum, and Nomismoceras rotiforme. No considerable development of passage-beds occurs, for a bed of black crinoidal limestone, crammed with brachiopods, is exposed a few yards from the lowest exposure of Pendleside Shales, and below this level no shale is found in the limestone-series. Underlying the black crinoidal limestones is a series of compact, greyish limestones, slightly cherty, and relatively unfossiliferous, but yielding corals typical of the Cyathaxonia-subzone.

VI. LOCAL UNCONFORMITY BETWEEN THE CARBONIFEROUS

LIMESTONE AND THE PENDLESIDE SERIES.

Throughout the Midland area generally, wherever the succession has not been broken by faulting, the absence of a physical break between the Carboniferous Limestone and the Pendleside Shales is clearly evident. Of considerable interest, therefore, is the proof. of a local unconformity between the two divisions, furnished by a section in the eastern part of the area.1

This section is found in a quarry near Old Mill, beside the Bakewell-and-Winster road, rather more than a mile east of Youlgreave. Fig. 5 (p. 62) is reproduced from a photograph of the section, taken by Mr. H. H. Arnold-Bemrose, who kindly made a special visit to the quarry for the purpose. The black shales of the Pendleside Series, containing Posidoniella lavis, are here seen to rest with unconformity on the limestones of the Lonsdaliasubzone. The shales, which show no sign of disturbance, rest evenly upon a surface formed by the truncated edges of the limestone-beds.

This section affords evidence of local earth-movement and erosion, contemporaneous with the deposition, in other parts of the area, of the uppermost beds of the Carboniferous Limestone or the lowest beds of the Pendleside Series. The limestones in the section represent a high level in the Lonsdalia-subzone. The absence of the Cyathaconia-Beds may be due, either to their removal by denudation during early Pendleside-time, or to the locality having formed land during Cyathaxonia-time.

1 Previous to the commencement of my work in the Midland area, Mr. C. B. Wedd had discovered and investigated a somewhat similar example of local unconformity at Darleybridge, a few miles distant from the section here described. His description is not yet published. (But see the Discussion on the present paper, p. 81.)