A. The Polycystine marl of Barbados appears at different parts of the island to present greater variations in its petrographical and zoographical composition than would appear from Ehrenberg's description (1875, L. N. 25, pp. 106-116). Through the kindness of one of my former students, Dr. Dorner, to whom I take this opportunity of expressing my thanks for the favour, I received a large number of specimens of Barbados rock, taken from various parts of the island, and they exhibit very great variations in their external appearance, their chemical composition, and the {clxxi}Radiolaria which they contain. The white specimens resembling Kieselguhr contained approximately 60 to 70 per cent. by volume of Radiolarian shells, the yellowish marl 40 to 50 per cent., and the brown and black (bituminous) marl 10 to 20 per cent. or less. Two analyses of the first, which my friend Dr. W. Weber was good enough to carry out, yielded different results from those which are given by Ehrenberg on the basis of Rammelsberg's analyses (L. N. 25, p. 116). The results of both are here given for comparison. --------------------------------+--------------------------+------------- Ehrenberg-Rammelsberg | Weber I. | Weber II. (Fragment from Hillaby). | (Chalk-like Fragment). |(Tripoli-like | | Fragment). --------------------------------+--------------------------+------------- Silicate of alumina, 59.47 |Silica, 52.2 | 71.3 Alumina and oxide of iron, 1.95 |Alumina (with traces | Calcium carbonate, 34.31 | of oxide of iron), 12.3 | 11.2 Water, 3.67 |Lime and magnesia, 31.9 | 14.8 |Carbon dioxide, 3.2 | 2.7 ______ | _____ | _____ Total, 99.40 | Total, 99.6 | 100.0 --------------------------------+--------------------------+------------- For further comparison I here add the three different analyses of Miocene Tripoli-marls from Sicily, given by Stöhr on the authority of Fremy, Schwager, and Mottura (Tagebl. d. fünfzigsten Versamml. Deutsch. Naturf. u. Aertzte in München, 1877, p. 163).