Assessing natural variation and the effects of charring,burial and pre-treatment on the stable carbon and nitrogen isotope values of archaeobotanical cereals and pulses

The aim of this study is to assess the potential of charred archaeobotanical cereal grain and pulse seed δ¹³C and δ¹⁵N values to provide evidence of crop growing conditions and as a potential component of palaeodietary studies. In order to reliably interpret archaeobotanical δ¹³C and δ¹⁵N values it is necessary to take into account the impact of charring, burial and laboratory pre-treatment procedures. We examine the effects of charring and burial on bulk δ¹³C, δ¹⁵N, %C, %N and C:N ratios in modern cereal and pulse material, and of cleaning by acid–base–acid (ABA) pre-treatment on modern and archaeobotanical charred material. Our study utilised bulk grain and seed samples to help account for within-ear/pod and between-plant variability in δ¹³C and δ¹⁵N values. Heating at relatively low temperatures and for prolonged times (230 °C for up to 24 h) is conducive to the formation of well preserved, undistorted charred cereal grain and pulse seed. Heating for 24 h has a systematic and predictable effect on δ¹⁵N values, with increases of around 1‰ on average in cereal grains and pulse seeds, and no consistent impact on δ¹³C values. Increases in δ¹⁵N are likely due to the loss of lighter ¹⁴N via N-containing volatiles. Burial (for up to 2 years) and ABA pre-treatment have no significant effects on δ¹³C or δ¹⁵N values. After pre-treatment, however, the %C and %N contents of the archaeobotanical material more closely resembles that of the modern charred grains and seeds, suggesting that archaeobotanical remains accumulate non-structural material during burial but retain their original carbon and nitrogen content. Therefore %C, %N contents and C:N ratios can provide useful criteria for assessing archaeobotanical preservation.     

On Trial—Social Relations of Map Production in Mid-Nineteenth-Century Britain

ABSTRACT

This article examines the social relations of map production in mid-nineteenth-century Britain with reference to moments when maps and their makers were ‘on trial’—legally in court in Edinburgh in 1853 and by public opinion in London in 1854 following a lecture. The principal protagonists include Alexander Keith Johnston of the map firm W. & A. K. Johnston, the German cartographer August Petermann, the mapseller Trelawney Saunders and John Bartholomew junior of the Bartholomew map firm. The article draws upon Thomas Gieryn’s idea of the ‘truth spot’ and on Matthew Edney’s call for studies in processual map history.