The Serra de Araripe, or that which runs between Crato and Barra do Jardim, is only an eastern branch of an elevated table-land which stretches continuously from the sea-coast, southward, and forms a natural boundary between the two great provinces of Ceará and Piauhy. It is generally elevated from 500 to 1,000 feet above the level of the country to the east of it, but not so much above that to the west; to this range the name of Serra Vermelha is given by the Portuguese, and Ibiapaba by the Indians. Between the 10th and 11th degrees of latitude it takes a westerly direction, and in about 47° of longitude takes a northerly sweep, finally terminating at the mouth of the River Amazon, under the equator, the country which it surrounds forming a valley of great extent, including the entire provinces of Piauhy and Maranham. This elevated range varies much in breadth, as many branches run off from it, both to the east and to the west; the top is nearly perfectly level, forming, as before mentioned, what the Brazilians call Taboleiras. The great mass of the Serra consists of a very soft, whitish, yellowish, or reddish-coloured sandstone, which in many places must be more than six hundred feet thick; and in this rock exist the nodules which contain the fossil fishes. The circumstance that first led me to suspect this rock belonged to the chalk formation, was an immense accumulation of flints and septaria similar to those of the chalk of England, which I found on the acclivity of the range during a journey made along its base to the north of Crato. I now began to inquire if anything like chalk was found in the neighbourhood, when I learned there were several pits in the Serra, whence the inhabitants obtained it for the purpose of white-washing their houses; these pits I afterwards found to be situated in a deep layer of red-coloured diluvial clay, which lies immediately over the sandstone of the Serra. In a ravine near Crato I endeavoured to ascertain the formation on which the sandstone rested, when I found it to consist of several layers of more or less compact limestones and marls, with a bed of lignite about two feet thick; upon what these rested I could not at that time ascertain, but some time afterwards when I crossed to the west side of the range, I found these limestones existing upon a deposit of very dark-red coarse-grained sandstone, abounding in small nodules of iron-stone. Thus we find that the structure of the rocks in this locality is very similar to that of the chalk formation in England; there is 1st. A ferruginous sandstone deposit, equivalent to the lower green sand or Shanklin sand. 2nd. A deposit of marls, soft and compact limestones, and lignite, equivalent to the English gault. 3rd. A very thick deposit of fine-grained, soft, variously coloured sandstone, containing Ichthyolites, equivalent to the upper green sand of England.