Professor Colin Lewis of Rhodes University, Grahamstown, South Africa, revisited St Helena for three weeks in May and June this year. Last year he delivered a public lecture under the auspices of The National Trust on evidence for climate change. He also collected bone and other samples from sediments in Fisher’s Valley, Prosperous Bay valley and Sandy Bay valley in order to date former climatic and environmental events on our island, Professor Lewis now reports as follows:

“Among the samples I collected last year, with the aid of Edward Thorpe, were bones collected about 7 m below the surface of unconsolidated sediments in Prosperous Bay valley. At least another 4 m of unconsolidated sediment existed beneath those bones, but bedrock was not exposed and those soft sediments may have been considerably over 4 m deep.

The bones were too fragmentary for full identification, but Professor Adrian Craig of Rhodes University, who specialises in ornithology, was satisfied that they were bird bones. I sent them to the Quaternary Dating Research Unit in Pretoria and they were discovered to be over 4,000 years old (the exact radio-carbon age will be quoted in the formal scientific publication). This means that the unconsolidated sediments that underlay them were deposited more than 4,000 years ago.

In 1975 Storrs Olson, in his masterly paper on the ‘Paleornithology of St. Helena Island, South Atlantic Ocean’, suggested that bird bones in Prosperous Bay valley’…are obviously very recent [in age].’ Ashmole (1963) had already suggested that these deposits were ‘probably hundreds rather than thousands of years old.’

Olson wrote that ‘In most instances, bones were lying exposed on weathered deposits of sediment and needed only to be picked up.’ He dug into some of the deposits in Prosperous Bay valley, but there is no indication that he collected bones from any great depth. Ashmole (1963) also appears to have collected from surficial sediments.
Olson (1975) suggested that bird bones in Prosperous Bay valley were younger than those at other sites he examined on St Helena. Chemical analyses by Dr P. E. Hare (reported in Olson, 1975) confirmed that the bones submitted to him by Olson from Prosperous Bay valley appeared to be younger than bones Olson submitted from other sites (Sugarloaf (two sites), Dry Gut): ‘the bones from Prosperous Bay had appreciable amounts of collagen, whereas those from Sugar loaf Sites 1 and 3 and Dry Gut did not.’

Hare divided the bones submitted to him into three time periods, those from Prosperous Bay valley being the most recent, Sugar loaf Site 3 and Dry Gut being of middle period, and Sugarloaf Site 1 being the oldest. He cautiously stated that ‘Specimens from both the middle and oldest periods…are more altered from the original bone than a sample…from Maryland [USA] of approximately 60,000 years old…they date from well back in the Pleistocene.’

Barnes (1817) stated that, at Sugarloaf, ‘small bones and eggshells’ exist in ‘a dark, friable earth, two or three feet in depth’ on top of limestone [shell-rich sand]. Darwin (1844) also wrote that ‘the bones of birds’ exist in ‘the upper beds of the limestone’ in a quarry on Sugar-Loaf Hill. If these bones and eggshells exist in ‘the limestone’ [shelly-sand] they may, as Hare’s findings suggest, be of Pleistocene age. The Pleistocene ended about 11,000 years ago and was succeeded by the Holocene, in which we still live.
The date obtained from the 7 m deep sample in Prosperous Bay valley proves that at least some of the bones in that valley are ‘thousands of years old’. Since the sediments in which they were deposited were water-laid it also shows that wet conditions existed in the mid-Holocene.

During this year’s field work (2005) samples were collected from near the surface in Prosperous Bay valley in order to ascertain the youngest age at which appreciable amounts of water-laid sediments were deposited in that valley. Other bird bones were collected form sites on Sugarloaf, Dry Gut, Potato Bay and in the vicinity of  Lot’s Wife’s Ponds, while mammal bones were collected in Sandy Bay valley. The stratigraphy was recorded at all these sites. Emma Bennett very kindly provided modern fish bones (Chubb Mackerel) that will be used as a control in radio-carbon dating.
The next stage in this research is the submission of the bird bones to Dr Philip Ashmole for identification. They will then be sent for radio-carbon dating, which should indicate the time-periods at which different birds and different climatic conditions existed in St Helena, and should show whether or not the oldest bones are of Pleistocene age. (My suspicion is that they are not!).

Unfortunately, this year, I did not find any more bones at appreciable depth in Prosperous Bay valley, although I worked there in miserably wet conditions and more leisurely research under more clement conditions might well show that they exist. If the access road for the proposed airport is built through the lower part of Prosperous Bay valley and the adjoining valley leading to the Signal Tower, it is likely that road building excavation will reveal bone samples at a variety of levels and in a variety of sediments. I hope that, if this occurs, the developers will fund a full scientific study of these remains, since St Helena is located in a crucial mid-ocean area and should provide palaeo-climatic information that will aid scientific understanding of the global oceanic current circulations which are believed to drive global climates.
I thank Dr David Kewn for accompanying me on most of my collecting trips, the National Trust, Miss Peters and her staff and Mrs Bennett in the relevant government departments for their support, and His Excellency, the Governor, for his interest in this important project.

Colin A. Lewis, June 2005.

References
Ashmole, N. P. (1963) ‘The extinct avifauna of St Helena Island’, Ibis, 103b, 390-408.
Barnes, J. (1817) A tour through the island of St Helena, Richardson, London.
Darwin, C. (1844) Geological observations on the volcanic islands visited during the voyage of H. M. S. Beagle, Smith, Elder and Co., London.
Olson, S. L. (1975) ‘Paleornithology of St. Helena Island, South Atlantic Ocean’, Smithsonian Contributions to Paleobiology, 23, 49pp.

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