TRANSACTIONS Vol.II, Part 1 1953 Editor - J. W. HESLOP HARRISON, D.Sc., F.R.S. King's College, Newcastle upon Tyne. CONTENTS PAGE The Magnesian Limestone Area of Durham and its Vegetation. By J. W. Heslop- 1 Harrison, D.Sc., F.R.S., and J. A. Richardson, MSc The Genus Rubus in Northumberland and Dnduun. By Yolande Heslop-Hanison 29 A Long Pollen Diagram from Northumberland. By Katbleen B. Blackburn 40 On the Occurrence of the "Upper Forest layer" around Cold Fell, N. Pennines. By 44 Job. Precbt Price: Five Shillings and Sixpence. Post Free. Printed by T. & G. Allan (Newcastle) Ltd., 289.291 Westaate Road. THE MAGNESIAN LIMESTONE AREA OF DURHAM AND ITS VEGETATION J. W. HESLOP HARRISON, D.Sc., F.R.S. AND J. A. RICHARDSON, M.Sc. I. INTRODUCTORY Although records of flowering plants from the Magnesian Limestone areas of Durham exist in Stephen Robson's "British Flora" (1777), it was not until the last two decades of the eighteenth century that the flora of these districts was subjected to intensive study. During that period, Winch, Thornhill and Waugh began the investigations which resulted in the production of their "Botanists' Guide through the Counties of Northumberland and Durham". This classical publication, considering the early date (1805), and the state of communications at the time, was a remarkable piece of work for, in addition to other notable plants, it lists a considerable percentage of the calcicole plants on record for East Durham. However, researches in the vegetation of the latter district did not cease with this book. In 1838, Winch was in a position to publish his famous "Flora of Northumberland and Durham" in Volume II of the Transactions of the Natural History Society of Northumberland, Durham and Newcastle upon Tyne in which there was set out an adequate account of the vegetation flourishing on the Magnesian Limestone. Soon after this work appeared, in 1846, the Tyneside Naturalists' Field Club came into being. This was a vigorous body which took its title seriously and organized field meetings to investigate those parts of the two counties noteworthy from the botanical standpoint. Amongst such areas, in the first ten years of its existence, the club visited the Magnesian Limestone outcrops on no fewer than ten occasions. This work continued until 1868 when Baker and Tate's "New Flora of Northumberland and Durham" was produced in Volume II of the Natural History Trans- actions of Northumberland and Durham. This work served to emphasize the thoroughness with which the early workers had investigated the plants of the east Durham calcareous soils. Subsequently, the Natural History Society and the Tyneside Naturalists' Field Club continued these researches until 1924 when the Northern Naturalists' Union, in conjunction with the former body, began to assist in the work. It is a significant fact that its very first field meeting (July 5th, 1924) was planned to examine Hawthorn Dene and cliffs as far south as the Foxhole Dene. Moreover, over a considerable number of years, many similar excursions have been made by the Union to Magnesian Limestone localities, as well as others carried out by keen individual workers. 1 Recently, Lousley (1950), dealing with our Magnesian Limestone tracts, asserted that, unfortunately, the only recent papers available were a few short notes in the Vasculum, but this is not the case, for in 1939, one of us (J.W.H.H.) in collaboration with Mr. G. W. Temperley brought together all the plant records for the area in a "Flora of the Three North- ern Counties". During the past four years we have been re-examining the ground to extend and confirm the observations of the early workers. The tloristic results of these labours are set out below. II. A GENERAL CONSIDERATION OF THE AREA Magnesian Limestone, as its name sufficiently indicates, is a limestone containing magnesium carbonate. But, whilst the rock is definitely of dolomitic tendencies, it must not be supposed that the ratio between the quantities of calcium carbonate and magnesium carbonate present remains constant. As a matter of fact, in specimens originating in Durham the amounts of the latter compound they contain may tluctuate between 0 and 44.9 per cent. Moreover, its structure and outward appearance display a range of variation such as is exhibited but rarely by any other British rocks. For instance, it may appear as a compact limestone, as a small-grained crystalline dolomite like that found in Castle Eden Dene, near the Blackhall Rocks and elsewhere on the coast, as irregular earthy masses amongst more stony rocks, as a limestone with a laminated structure such as is prevalent in the quarries near Sunderland and at Marsden, as a pseudo-brecciated rock occurring at Frenchman's Bay and so on. In Durham the Magnesian Limestone formation occupies a roughly triangular area of 230 square miles, bounded in the east by the cliffs on the coast between South Shields and Hartlepool. To the west, as it traverses the Coal Measures, its limits are clearly defined by a broken line of eminences, of varying heights, indented by numerous irregular "bays" produced by denudation. These hills are seen at their best at Cleadon, West Boldon, Penshaw Hill, Sherburn Hill, Strawberry Hill, Old Cassop, Quarrington Hill, Coxhoe, Merrington, Westerton, Eldon, Midderidge, East and West Thickley, Redworth, Killerby, Headlam and the White Cross. South of this, the Magnesian Limestone leaves the county to pass into Yorkshire. Although the escarpment never attains really great elevations, it displays considerable changes in level as it proceeds southwestward. Thus, from South Shields to West Boldon, it varies from heights less than 100 feet to 300 feet; thence it runs on to Thrislington and shows elevations up to 550 feet. Continuing southward, it reaches 644 feet at Westerton, 540 feet at Eldon, 400 feet at East Thickley and then its maximum of 650 feet just west of Redworth. At Pierce Bridge where it crosses the Tees into Yorkshire it falls to a height of 231 feet. 2 3 The third side, or base line of the triangle, is greatly obscured by drift, but it curves from West Hartlepool past Wynyard Park, Grindon and Stillington to strike the Tees south of Darlington. East of the escarpment, the Magnesian Limestone breaks into a series of low undulating hills relieved at intervals by less broken stretches. Toward the coast line, these are intersected by a number of deep denes or ravines of various lengths. Sixty years ago these were veritable beauty spots. Through each, great and small alike, flowed its own crystal- clear stream. In the more confined and narrower ones these ran along the base of steep slopes clad with almost impenetrable thickets of mixed vegetation. In some of the more important denes, like Castle Eden Dene, the burns, in their upper reaches were walled between precipitous cliffs supporting an abundance of rare flowering plants and ferns. Lower down, the denes merged into broader valleys with their slopes covered with the mixed ash woods characteristic of the Magnesian Limestone. However, the advent of the railway rudely disturbed these wood-land solitudes, and the destruction then commenced was speeded up by the sinking of three modern collieries at Easington, Horden and the Blackhall Rocks. Almost immediately, on the stretch of coast between Easington and the Coastguard Station, no fewer tban four of the dene most productive of botanical and entomological rarities were over-whelmed on the landward ends by debris from the mines. To complete the catastrophe, in the richest of these, the coal refuse caught fire, with the result that the dene was smothered by dense clouds of noxious fumes. Further, the cuttings and the embankments necessitated by the construction of the new Easington- West Hartlepool road, carried the work of destruction farther inland to destroy additional stretches of the larger denes, to obliterate some of the smaller ones entirely and to initiate movements destined to destroy utterly the seaward portion of Crimdon Dene. In spite of the widespread devastation outlined above, the more picturesque parts of Castle Eden Dene, the whole of Hawthorn Dene and much of Hesleden Dene remain in a more or less satisfactory con- dition. Their vegetation still provides a source of pleasure to the enthusiastic botanist. In addition, with the extinguishing of the burning pit debris and the cessation of promiscuous tipping, many of the minor denes show encouraging signs of recovery. The latter possibility, with the probable taking over of Castle Eden Dene by the Nature Conservancy, fills us with renewed hopes that future naturalists will be enabled to write, not of the "Doom of the Denes" as Wm. Carter was constrained to do in 1924, but of their rehabilitation. 4 Finally, along the coast there stretches a long line of Magnesian Limestone cliffs providing diverse habitats, which, in spite of repeated firing, still maintain their peculiar florulae, described amongst others, below. III. THE FLORULAE OF SPECIAL HABITATS Taking the Magnesian Limestone tract as a whole, owing to the soft and friable nature of the rock, it has produced soils, which, in spite of their comparatively unproductive nature, have been under cultivation for a very long period. Thus the actual areas in which the vegetation remains in a reasonably undisturbed condition, and therefore available for study, are quite small. In fact, in addition to those listed in the previous section, very few are left except certain stations on the escarpment too rough for cultivation, small woodlands, bank sides, rough pastures, limited zones around quarries and, paradoxically enough, the quarries themselves. Rough Pastures Of the rough pastures remammg, we have examined a long series situated at Cleadon, Houghton, Pittington, Elemore, Strawberry Hill, Hawthorn, Easington, Cassop Vale, Black Hall Rocks, Old Quarrington, East Hetton and Raisby and elsewhere.