The Ngovo Group: an industry with polished stone tools and pottery in Lower Zaïre

Summary Now, for the first time, it is possible to place in an exact archaeological context the polished tools which have been collected for many years on the surface in the savanna immediately to the south of the equatorial forest. In Lower Zaïre, in an area of 6000 km², polished tools have been found systematically associated with a particular type of pottery. This pottery, which was previously known as Groupvi pottery and which we propose calling Ngovo group pottery is very distinctive.Although faunal remains associated in one case were of wild animals, someElaeïs andCanarium nuts could indicate the beginnings of agriculture. A series of dates in good agreement place these polished tools and this pottery within the last two centuries bc.At the present time, iron-working in Lower Zaïre has not been dated prior to the second century ad. This Early Iron Age is associated with the Kay Ladio group pottery which is possibly derived from the Ngovo group.

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Résumé Pour la première fois, il est possible de préciser le contexte archéologique des outils polis que depuis longtemps on recueillait en surface dans les savanes immédiatement au sud de la forêt équatoriale.Au Bas-Zaïre, dans une zone de plus de 6000 km², des outils polis ont été trouvés systématiquement en association avec une céramique d'un type particulier. Cette céramique, connue précédemment sous le nom de céramique du groupevi et que l'on propose d'appeler dorénavant groupe de Ngovo, est très caractéristique.Bien que les restes de faune qui y sont associés dans une grotte soient ceux d'animaux sauvages, des noix d'Elaeïs et deCanarium indiquent peut-être un début d'agriculture.Une série de datations remarquablement convergentes placent ces outils polis et cette céramique durant les deux derniers siècles bc.La métallurgie n'est jusqu'à présent pas datée au Bas-Zaïre avant le 2e siècle ad. Cet âge du fer ancien est associé à la céramique du groupe Kay Ladio qui dérive peut-être du groupe de Ngovo.

     

Aggregation of Sampling Units: An Analytical Solution to Predict Variance

Geographical variables generally show spatially structured patterns corresponding to intrinsic characteristics of the environment. The size of the sampling unit has a critical effect on our perception of phenomena and is closely related to the variance and correlation structure of the data. Geostatistical theory uses analytical relationships for change of support (change of sampling unit size), allowing prediction of the variance and autocorrelation structure that would be observed if a survey was conducted using different sampling unit sizes. To check the geostatistical predictions, we use a test case about tree density in the tropical rain forest of the Pasoh Reserve, Malaysia. This data set contains exhaustive information about individual tree locations, so it allows us to simulate and compare various sampling designs. The original data set was reorganized to compute tree densities for 5 times 5-, 10 times 10-, and 20 times 20-meter quadrat sizes. Based upon the 5 times 5-meter data set, the spatial structure is modeled using a nugget effect (white noise) plus an exponential model. The change of support relationships, using within-quadrat variances inferred from the variogram model, predict the spatial autocorrelation structure and new variances corresponding to 10 times 10-meter and 20 times 20-meter quadrats. The theoretical and empirical results agreed closely, whereas neglecting the autocorrelation structure would have led to largely underestimating the variance. As the quadrat size increases, the range of autocorrelation increases, while the variance and the proportion of noise in the data decrease.