Neutron scattering studies have indicated that the non-coordinated water at smectite surfaces has a similar mobility to that of bulk water, but that the water coordinated to the cations is immobile on the time scale of the neutron measurements. Thus hydrophylic polymers can readily displace the non-coordinated water and bind to the silicate surface, and to the exchangeable cations through a water-bridge mechanism. Poly(ethylene oxide) molecules with molecular weights up to 4000 appear to be bound to Na-montmorillonite in flattened conformations at the clay surface. Poly(vinyl alcohol) is extensively bound by Na-montmorillonite and by Na-Laponite (a synthetic hectorite-like clay); as binding progresses fewer molecule segments can contact the surface and so at the higher levels of adsorption extensive loops of polymer extend away from the silicate surface. Some polyanions provide good protection for smectites against flocculation with salt. The abilities of such polymers to protect the clays is dependent both on the extents of the charges and on the solution conformations which these polymers can assume.

Lake Ejagham is a small, shallow lake in Cameroon, West Africa, which supports five endemic species of cichlid fishes in two distinct lineages. Genetic evidence suggests a relatively young age for the species flocks, but supporting geologic evidence has thus far been unavailable. Here we present diatom, geochemical, mineralogical, and radiocarbon data from two sediment cores that provide new insights into the age and origin of Lake Ejagham and its endemic fishes. Radiocarbon ages at the base of the longer core indicate that the lake formed approximately 9 ka ago, and the diatom record of the shorter core suggests that hydroclimate variability during the last 3 millennia was similar to that of other lakes in Cameroon and Ghana. These findings establish a maximum age of ca. 9 cal ka BP for the lake and its endemic species and suggest that repeated cichlid speciation in two distinct lineages occurred rapidly within the lake. Local geology and West African paleoclimate records argue against a volcanic, chemical, or climatic origin for Lake Ejagham. Although not conclusive, the morphometry of the lake and possible signs of impact-induced effects on quartz grains are instead more suggestive of a bolide impact.

At altitudes below 1300 m most species of grasses in tropical Africa are ones that use 4-carbon photosynthesis. Above 4000 m only species of the subfamily Pooideae using 3-carbon photosynthesis are found. At intermediate altitudes the percent of 3-carbon genera and species in the grass flora is a very regular function of altitude. The correlate of altitude that controls the distribution of grasses appears to be temperature. Fossil grass cuticles are identifiable to genus and should provide a useful paleothermometer. If no other errors were involved, the regular altitudinal distribution of genera in the flora of tropical East Africa would permit paleotemperature estimates with 95% confidence limits of ± 1.2°C.