Rochas-mater da "terra roxa"

Abstract

SUMMARY Physico-chemical and mineralogical studies of the of the Sao Paulo State by the Soil Division of The Agronomical Institute proved the existence of different in and its origin from basaltic rocks. The Brasilian denomination terra is already many times translated to which is inexact, because the colour roxa corresponds to violet in English. We must insist on the perfection of Brasilian expression, which gives the shortest and the best characteristic of the true soil, derived through the decomposition of basalts and diabases in the Sao Paulo State. The term originated much confusion, because there are in this state many soils of different origins, but the true soil is guite unique. The colour of this soil appears very beautifully on the clean fields above the diabase hills at the distance of some hundreds of meters. In the state of complete dryness the soil becomes coffee brown, but never gets a red colour. The soil is the best soil of South America, on the contrary the red soils, which are mostly lateriuc, are bad soils. Some exceptions, do exist, of course. The basalts produce laterites and other red of better qualities. With the purpose to contribute to the study of the and the red the present essay was made, describing the basic rocks of South-Brasil, as mother rocks of soils. The basic monograph of Djalma Guimaraes Magmatic Province of South-Brasil (5), many times mentioned in the petrographic literature, definitively established the prin­cipal types and the mineral-components of triassic basic rocks in South-Brasil. We have found some varieties of basic rocks, not yet known, but considered important for the question of and red soils. To soil science we consider of importance the discovery of acid melaphyres without labradors, which are essential for all other basaltic rocks, with exception of most basic and extreme types.