Lignite

In Ribeiro do Meio, in the valley of S. Jorge, about 300 meters above sea level, two veins or deposits of impure lignite have been known for many years. This lignite is associated with different layers of tuff and clay, in one of which abundant fossil leaves of Dicotyledons and Ferns were found. As a thick layer of basalt and slag, over 300 meters high, lies on top of the deposits, it seems evident that there was once abundant terrestrial vegetation at the site, long before the volcanic formations that cover it.

The nature of the tuffs that accompany the lignite and some of the nearby conglomerates authorize, according to Lyell, the admission that near the site where the deposits exist, there were once a series of eruptions. Therefore, it is not impossible that the same lignite and leaves had accumulated in a crater, and that the erosion of the valley later exposed them.

It is said that the analysis of the lignite of S. Jorge revealed 60 percent coal and 30 percent ash.

This lignite, which had been buried for many years due to landslides of the upper terrains, was again uncovered in 1917. See Deposits of leaves and Phanerogams.