Expedição à Região Centro Ocidental da Bahia

Resumo

In this article, the author, Engineer Gilvandro Simas Pereira, of the Brazilian National Council of Geography discusses the organization and planning of the scientific expedition which traversed the West Central Region of Bahia under his direction. Subsequently he presents some interesting geographical conclusions about this region which includes the municipalities of Barreiras, Ang'cal, Cotegipe, Santana and part of the municipalities of Barra, Bom-Jesus da Lapa. Santa Maria da Vitória and Correntina.

            He begins with a description of the trips to the region which he names “gerais” and tells of the difficulties which the topographic groups encounter on their field trips. Here they ran into the first large divergence between the reality and the very rough maps available. According to the latter, the river Mosquitinho runs directly to the rio Grande, whereas in reality it runs to the rio das Fêmeas which is a tributary of the Grande.

            The landscape of this region is studied in the zone consisting of great campinas which divides the Tocantins - São-Francisco waters. The author tries to explain the genesis of the sandstone sediments of the dividing section attributing their origin to a shallow sea of the cretaceous age. Then he explains the present contours of the relief, showing them to be due to the combined action of the wind, rain and the rivers.

            Next he describes the caatingas, the second large unit, first telling of the field trips of the groups and afterwards making geographic observations. His interpretation of the genesis of the Silurian rocks which constitute the soil of these caatingas is that they originated in the depths of the great Silurian sea. Next he describes the quaternary sediments delimiting their extent; he shows that the initial impression which the traveler has of vast forests is erroneous, for the forest is really but a narrow band bordering the river and 100 meters from the river gives way to the caatinga. He studies the Archean formation of the surroundings of the Correntina and raises the problem of the paleogeographic nature of this outcropping and explains it as an island of the Silurian sea.

            In another chapter, the author reviews the methods employed in the surveys, and also describes the various instruments utilized for altimetric observations and the control of annotations by means of a mercury barometer in the office. Besides explaining the instruments for the planimetric work he tells how the distribution of errors is handled and· how the points for measuring distances are determined by astronomic coordinates.

            Further on the author deals with the human geography of the region, examining the main centers of which the first is Barreiras. He outlines the cause of its development as the main center of the west of Bahia. Then he analyses the cities of Santa Maria da Vitória, Santana and Correntina, observing various problems which the latter present. He also studies the lesser centers such as villages and tiny settlements and even the farms, and carefully considers the very important problems of communication and transportation.

            In conclusion the author shows the considerable cartographic changes made, mentioning the discovery of the Jatobá river as well as a large number of other modifications.