A statistical method (Benzécri's Factorial Analysis of Correspondances) is used to study the distribution of microarthropods in mosses growing on a forest rock and in surrounding soil. 26 species of Insects (Collembola) and 45 species of Acari (Oribata) were investigated.Comparison of data shows a graduate variation of the population from the soil itself to the aerial mosses, passing by soil mosses.A population gradient is shown from dry and highly drained mosses of south face of the rock to the deep edaphic biotops of the north face. Relative specific affinity for the various samples makes conspicuous their ecologic specialization and the importance of humidity and temperature as distribution factors. A continuous variation of biotops is characterized by a continuous variation of populations.