The whole of the country around Rio is essentially granitic, all the rocks being of that nature to which the name of Gneiss-granite has been applied, from their possessing decided marks of stratification. The mountains generally run in chains having no particular direction, and are of all sizes, from slight eminences to mountains which rise from 2,000 to 3,000 feet above the level of the sea. The loftier of these mountains, such as the Peak of Tejuca, the Corcovado, and the Gavea, have their south-east sides bare and precipitous, while those to the northward have a gradual ascent, and are wooded to their summit. Notwithstanding the enormous length of time which the sides of these mountains have been covered with their mighty forests, the alluvial layer of soil which rests on them is very thin. This, however, may be accounted for by the heavy rains washing it, as well as the materials from which it is formed, down into the valleys, where the alluvium is often found to be many feet deep. Hence it is that the deep valleys which intersect the mountain ranges are the principal seats of agricultural industry; and some of them, particularly in the vicinity of the city, are thickly studded with habitations, surrounded with plantations of Coffee, Oranges, Bananas, and Mandioca. Many of the lower hills near the city are now also cleared and planted with Coffee, but the plantations were too young when I left to form any idea of their success at so low a level. Beneath the alluvium there is a bed of reddish-coloured clay, which is very tenacious when wet. It is often from thirty to forty feet in thickness, and is not peculiar to the province, as I have met with it in every part of Brazil where I have travelled. It frequently contains numerous boulders, consisting of rounded, as well as angular, fragments of Gneiss, Granite, and Quartz, and is often inter-stratified with various beds of sand and gravel. It is obvious then from these observations, that the soil around Rio itself is not generally rich. Indeed, the first thing which strikes a stranger on his arrival, is the apparent poverty of the soil contrasted with the richness of the vegetation. But for the humidity of the atmosphere, the heavy dews of the dry season, and the rains of the wet, combined with the heat of a tropical sun, the greater part of the country immediately surrounding Rio would not be worthy of cultivation. The very small quantity of soil which suffices for some plants is quite astonishing to a European. Rocks, on which scarcely a trace of earth is to be observed, are covered with _Vellozias_, _Tillandsias_, _Melastomaceæ_, _Cacti_, _Orchideæ_, and _Ferns_, and all in the vigour of life.