The Origin of the Broads

Abstract

IN an R.G.S. Research Memoir just published,1 a theory attributing the origi of most of the Norfolk Broads to certain natural ph siographical processes was advanced. Briefly, it postulated that the formation of the broads could be explained in terms of a geologically very recent marine transgression of the Norfolk river valleys, during which a thick wedge of estuarine clay was laid down over the earlier valley peats; the broads themselves were thought to have been initiated as discontinuous lakes, lying in natural hollows in the peat filled with water ponded back between the flanges of the clay and the upland valley margin (by-passed broads), or in tributary valleys whose mouths were blocked by the clay (side-valley broads). This theory was based mainly on stratigraphical data obtained by boring through the alluvial deposits of the Ant and Bure valleys, and, although certain difficulties of detail were admitted, the conclusions reached seemed to be in very general accordance with the evidence at the time of submission of the manuscript in December 1950. In conjunction with the physiographical work in the Bure valley, a vegetational survey was also made, in which the present pattern of the plant communities was related directly to the gross and detailed stratigraphy of the underlying deposits.3 Between 1950 and 1952, this combined vegetational and stratigraphical work was extended by one of us (J. M. L.) to the Yare valley. Here, the increasing emphasis on the detailed interpretation of the vegetation in terms of the stratigraphy has required progressively much more closely set lateral bores than were employed to give the general physiographical outline in the Bure and Ant valleys, and, arising from this, important new data have come to light calling for a major reconsideration of the earlier hypothesis of the origin of the broads. Convincing stratigraphical evidence has now been obtained to suggest that all the Yare valley broads are artificial. Their basins are formed by undoubted excavations, usually reaching down to 3 metres or more below the present surface level, and presumably representing hollows left by deep extraction of peat in historical times. This view is further supported by cartographical and other data. A reconsideration of the evidence previously available from the Ant and Bure valleys, supplemented by additional observations since made in certain critical areas, now suggests that this explanation is of general application for the origin of the typical by-passed broads as a whole, though reservations, through insufficient data, must still be made in respect of the less numerous side-valley broads. A full presentation of the new evidence, and an assessment of the relationship of the artificial basins of the broads to the natural stratigraphy of the valleys, will be made as soon as possible. In the interim, it should be emphasized that the greater part of the story of the natural evolution of the river valleys, as distinct from the origin of the broads themselves, remains substantially unchanged from that presented in the Memoir.