4th. The white chalk itself, and flints occurring in pits partially covered by red diluvial clay. Flints are very common along the foot of the Serra, to the N.W. of Crato, but none were found in any of the chalk-pits that I examined: I learned, however, that at a considerable distance to the north of Crato, at a portion of this mountain range, called the Serra de Botarité, both chalk and flints are far more abundant than they are near the former place, where they seem to have been almost entirely washed away, previous to the deposition of the red clay in which they are now found. Since the time when these rocks were first deposited at the bottom of the sea to the present period, both they and the surrounding country must have undergone various changes with respect to elevation; but before making any observations on this subject, I will point out the various places where I have met with traces of the chalk formation, besides that just described. In 1838, during my voyage up the Rio de San Francisco, which empties itself into the Atlantic between the 10th and 11th degrees of south latitude, I obtained specimens of the rock on which the Villa do Penêdo is built, and on comparison these proved to be identical with those from the upper sandstone of Crato. In 1839, I found the ferruginous sandstone of Crato extending westward thence about 500 miles, and in the year 1841 I observed at Maranham, in 2° of south latitude, and 44° of west longitude, a formation very similar to that at Crato. The whole island on which the city of Maranham is built, consists of a very dark-red ferruginous sandstone; on the main land to the westward, the same rock was observed rising a little above the sea level, but immediately upon it there exists a deposit, in some places more than 50 feet thick, of a yellowish and greenish coloured sandstone, very soft, and of a marly nature. From these data, then, I think there can be little doubt that the whole of that immense shoulder which forms the more easterly point of the American continent, has at one time been a great depository for the chalk formation. The only other rocks that I observed in places denuded of the deposits belonging to the chalk are, 1st, gneiss and mica-slate, the layers of which crop out in nearly a vertical direction, as was frequently observed on my journey from the coast, and during my voyage up the Rio de San Francisco; and, 2nd, beds of grey-coloured clay-slate, which I passed over about 18 leagues below Crato. The whitish coarse-grained sandstone that I met with immediately afterwards, is probably equivalent to the ferruginous sandstone found on the west side of the range; from this it would appear, that between the cretaceous series and the primary stratified rocks, there are no traces either of the carboniferous or the oolite formations, nor in any part of Brazil through which I afterwards travelled did I meet with any signs of them.[5]