A micromorphological study was carried out on five “Red Clay” soils series, located at the VII Region, Central Chile. An alteration sequence and organization of the soil fabric was stablished in these soils, derived from a saproliric or tobiferous material of andesitic-basaltic nature. This sequence begins with a fissu ring of rocks and minerals with deposition of ron into the fissu res, and plasma formation. The latter accumulates and organizes into soil fabric. Crystal layers of “Primary Vermiculites”, found in the oldest soils, open progressively up to disintegration, followed by the incorporation as plasma to the s-matrix. Clay illuviation with the formation of argilic horizons s the predominant genetic process, being more intensive in tlie San Clemente and Colbún soil series, evidenced by the abundance of well formed, thick and birefrigent argillans.