than Durlston Bay, Swanage. Slithering over the low bluffs at Peverill Point, they meet their first rocks in earnest in what is the Broken Shell Member of the Durlston Formation of the Purbeck Limestone Group. They may not have known this - nor does it really matter too much to the beginner - but this kind of analysis is now possible and available to the serious stratigrapher who needs to know such details, thanks to the appearance of an authoritative account of the type section of the Purbeck rocks of southern England (Clements, Proceedings of the Dorset Natural History and Archaeological Society, v. 114, p. 181, 1992). The bed units are neatly contained within the cliff and foreshore outcrops of Durlston Bay; but having said that, the details have never, until now, been presented in so clear a fashion, even by A. J. Arkell, who usually did things so meticulously and clearly.

Clements has spent over 25 years researching first the gastropod fauna of the Purbeck rocks and then the total ostracod fauna, as he was able to do under the guidance of Peter Sylvester-Bradley when he moved to Leicester in the early 1970s. Ostracods are quite important in Purbeck stratigraphy, having been the basis of an early zonation by Lye11 (1855) and T. R. Jones (1885) and, much later, the subject of a freshwater-brackish water cycle notion of palae- oecology by F. W. Anderson and Sylvester-Bradley. All these ideas are reviewed in passing in this definitive account, but it is the recording of the successions involved which make this contribution to British stratigraphy important. The fullest field notes

accumulated over the years are here annotated with additional notes on footprints (dinosaurs!), insects (world famous) and lithological highlights in sketched columns which are a model of clarity (Fig. 1). The pages of bed-by-bed descriptions are equally comprehensive, including a frequency value for gastropods and a rough number count for the ostracods in the same bed. Taken with other assess- ments of the palaeoecology of these same beds, others may now take up the debate as they judge the facts, including the Anderson ‘faunicycles’ which have sometimes perplexed micropalaeontologists.

The type section recently came under some discussion when there was debate over coastal defence works needed to protect the Swanage cliffs at the southern end of Durlston Bay. At the time, modern flats were threatened by continuous cliff falls in a fault zone. It was a case difficult to contest on human grounds; the loss of homes or the loss of fossils must have seemed ‘no contest’ to the general public, as, indeed, it was portrayed in the press both local and national. If anything, this present account must focus attention upon the importance of the geology involved. It might even raise the local awareness of the World Heritage status of the cliffs. As for that beginner-collector, he should at least now be able to say precisely where he collected his bivalves (crowded upon bedding surfaces to a degree which would make them hard to miss) in relation to geography and precise stratigraphy in Durlston Bay.

Correspondence

The Stonehenge bluestones - Ice Age or Bronze Age? Sirs: Graham and Judith Jenkins (Geology Today, v. 9, p. 87, 1993) raise once again the question of whether the exotic ‘bluestones’ that form part of Stonehenge were brought to Salisbury Plain by Ice Age glaciers or by the people of Bronze Age Wessex who built this great ceremonial structure.

I have written before in these pages (Geology Today, v. 7, p. 203, 1991) and elsewhere (Nature, v. 243, pp. 214-216, 1973) about the improbability of extensive glaciation in southern England. On Salisbury Plain, in particular, not only are there no exotic boulders to be seen, except those at Stonehenge and from Boles Barrow (now in Salisbury Museum), there is absolutely no evidence for the presence of exotic lithologies in any of the Pleistocene river gravels of the rivers draining Salisbury Plain. This is in striking contrast to catchments that are known to have been invaded by glacial ice during the Pleisto- cene. For example, in some places in the Thames valley, glacially derived material forms as much as half the Pleistocene terrace gravel. Graham and Judith Jenkins make no mention of this fairly conclusive indication that no glacial ice ever reached Salisbury Plain. In the last sentence of their recent article, they seem to indicate that, with the support of English Heritage, they are about to undertake a geophysical search for buried glacial erratics.

They suggest that in the late eighteenth and early nineteenth centuries Salisbury Plain was so encumbered with boulders that farmers had to bury them to clear their land. This suggestion seems to be based on the account by de Luc of his travels in England between 1777 and 1809, in which he reports the presence on Salisbury Plain of blocks of sarsen, granite and trap. It is difficult to know to what this account by de Luc refers or to reconcile it with the field and historical evidence on Salisbury Plain.

If durable rock types were ever common on Salis- bury Plain prior to the nineteenth century, why are none employed in early buildings? Where sarsen is available in Wiltshire, on the Marlborough Downs, it is widely encountered in mediaeval and post- mediaeval buildings. Similarly, where exotic rock types are present in southern England - for example, in the Selsey peninsula - they are found incorporated in early buildings. Why not on Salisbury Plain? There is no hint in topographic accounts at the time of de Luc’s visit that Salisbury Plain was other than an expanse of smooth turf given over almost entirely to the grazing of sheep: ‘In vain the eye looks round for some object to relieve the uniformity of the scene; all is flat, barren, desolate, nothing interposing between it and the distant horizon.’ (Warner, 1801, quoted in Chippindale, C. , Stonehenge Complete, 1983). There

GEOLOGY TODAY September-October 19931 177

is no mention of boulders or of farmers converting the sheep pastures to arable.

And what about early investigations of Stonehenge? Both Stukeley in the early eighteenth century and Cunnington in the late eighteenth century knew that the bluestones were of exotic origin. Both men knew Salisbury Plain intimately, having ridden over it frequently on horseback, and both were careful observers, as their written accounts of their archaeological interests attest. Yet Stukeley says of the bluestones: ‘brought somewhere from the west’; and Cunnington writes even more specifically: ‘brought from some part of Devonshire or Cornwall, as I do not know where such stones could be procured nearer than the latter places’ (both quoted in Chippindale, C., op. cit.). Both men were familiar with Salisbury Plain either before, or at the time of, de Luc’s visits to England. Can we believe that they failed to see a potential source for the Stonehenge bluestones on Salisbury Plain itself?

And finally, what of the socio-political context in which the bluestones were originally used, in Period I1 of the construction of Stonehenge? There is ample evidence that distinctive rock types had special significance in early societies and were brought over considerable distances, sometimes in substantial amounts, for purely ritual or ceremonial purposes. The rocks forming the facade of the great passage grave at Newgrange in County Meath have no immediate local source and must have been brought to the site by its builders. And in the recently reported work at nearby Knowth, also in County Meath (The Times, 14 September 1993), one of the discoveries associated with a late Neolithic ceremonial building is ‘the ritual deposits placed in niches cut into some of the post holes. The offerings include freshly mined flint from the coast of Antrim in Northern Ireland . . .’.

It is not difficult to believe that with the growing significance of communal monuments in the late Neolithic and early Bronze Age, ever more ambitious ritual undertakings would be attempted. Stonehenge, whatever the source of the stones, is itself convincing evidence of this development. In this context, the carriage of the 82 bluestones from south-west Wales to Salisbury Plain seems not only possible but likely, and no more difficult than the rather later carriage of the much larger sarsen stones to Salisbury Plain from the Marlborough Downs. These undertakings are perhaps best interpreted as symbolic displays of the spiritual authority and political power of the people of Wessex who conceived and executed this great work. What reason is there to underestimate their ambition

or to question their technical and organizational ability?

CHRISTOPHER GREEN Royal Holloway

Egham Surrey TW2O OEX

St Barbara in North Britain Sirs: I read with interest the article by Jonathan Selby (Geology Today, v. 9, p. 89, 1993). In 1990 I located a shrine with a plaque dedicated to St Barbara at Carfin Grotto, Newarthill Road, Carfin, Lanarkshire ML1 SAJ. The custodian of the shrine wrote to me: ‘Our shrine is dedicated to Our Lady of Lourdes and St. ThCrkse, although there is a marble plaque - more of a sketching - of St. Barbara and laid into the wall of the Grotto. This was erected by the “Catholic Miners’ Guild” and dedicated to all the “unemployed miners who helped to build the Grotto back in the 1920s”.’ (see sketch). Are any other dedications to St. Barbara known to your readers?

JOHN COOPER Department of Palaeontology

The Natural History Museum London SW7 SBD

SCOTLAND Correction The second item in the ‘Suggestions for further reading’ on page 106 of the

In future issues of Geology Today May-June issue of Geologv Today (v. 9, 1993) I Time flies: the geological record of Calcium carbonate cementation of should read: insects sandstones Picken, 1988. J. & Stone Timberlake, hammers S. 1 by Ed Jarzembowski & Andrew Ross by Niall Fleming

and firesetting. Bulletin of the Peak District Mines Historical Societv, v. 10. PLUS our regular items

_,

pp. 135-138. I

178lGEOLOGY TODAY September-October 1993