We have already seen that the country, from the coast to Crato, is for the most part level, large portions being covered with coarse white sand or gravel of various sizes, which give it the appearance of the dried up bed of an immense river; much of this gravel consists of flints, and intermingled with them are numerous boulders of various sizes, more or less rounded, consisting of granite, gneiss, and quartz. Whenever these gravelly tracts cease to appear, the surface of the country is covered with a deposit of the same kind of red clay which lies over the upper sandstone of the table-land. To the westward of this table-land, considerable portions are covered with the variously shaped iron-stone nodules, found in the ferruginous sandstone, and which have accumulated from the decay of that rock. I have now to offer a few remarks on the changes of elevation which this part of the continent has undergone since the chalk rocks were first deposited; it is manifest that that deposition took place at the bottom of a shallow ocean, and it admits of no doubt that at some subsequent period it has been gradually elevated above the level of the sea; it is evident that this elevation has been gradual, from the horizontal position of the strata of which the deposit is formed; for had the elevating cause been sudden and violent, their original position would not have been so perfectly maintained. The first portion that emerged from the sea was probably the long elevated table-land, which for a period must have formed a neck of land separating the Atlantic Ocean on the east, from the great bay which the immense valley to the westward must then have formed.