_June 30th._—On the 21st we left Rio on our way to the province of Minas Geräes, where we were to pass a week at the coffee fazenda of Senhor Lage, who received us so courteously on our former visit to Juiz de Fora, and who was so influential in projecting and carrying out the Union and Industry road. The journey to Juiz de Fora, though we had made it once before, had lost nothing of its beauty by familiarity, and had gained in interest of another kind; for his examination of the erratic drift at Tijuca has given Mr. Agassiz the key to the geological constitution of the soil, and what seemed to him quite inexplicable on our first excursion over this road is now perfectly legible. It is interesting to watch the progress of an investigation of this character, and to see how the mental process gradually clears away the obscurity. The perception becomes sharpened by dwelling upon the subject, and the mind adapts itself to a difficult problem as the eye adapts itself to darkness. That which was confused at first presently becomes clear to the mental vision of the observer, who watches and waits for the light to enter. There is one effect of the atmospheric influence here, already alluded to in the previous pages, which at first sight is very deceptive. Wherever there is any cut through drift, unless recently opened, it becomes baked at the surface so as to simulate stone in such a way as hardly to be distinguished from the decomposed rock surfaces in place, unless by a careful examination. This, together with the partial obliteration of the stratification in many places, makes it, at first glance, difficult to recognize the point of contact between the stratified rock and the drift resting above it. A little familiarity with these deceptive appearances, however, makes it as easy to read the broken leaves of the book of nature here as elsewhere, and Mr. Agassiz has now no more difficulty in following the erratic phenomena in these Southern regions than in the Northern hemisphere. All that is wanting to complete the evidence of the actual presence of ice here, in former times, is the glacial writing, the striæ and furrows and polish which mark its track in the temperate zone. These one can hardly hope to find where the rock is of so perishable a character and its disintegration so rapid. But this much is certain,—a sheet of drift covers the country, composed of a homogeneous paste without trace of stratification, containing loose materials of all sorts and sizes, imbedded in it without reference to weight, large boulders, smaller stones, pebbles, and the like. This drift is very unevenly distributed; sometimes rising into high hills, owing to the surrounding denudations; sometimes covering the surface merely as a thin layer; sometimes, and especially on steep slopes, washed completely away, leaving the bare face of the rock; sometimes deeply gullied, so as to produce a succession of depressions and elevations alternating with each other.