Two days after my arrival I paid a visit to Captain Antonio da Cruz, where I learned that on a rising ground between his house and the Serra, there were often found rounded limestones, which when split exhibited the remains of fishes; two of his sons accompanied me to the spot, where I made a collection of several species more or less perfect. The place where these were found was on the slope of a low hill about a mile from the Serra,—the stone in which they occur being an impure dark-coloured limestone: I found them of all sizes, but none larger than I could lift, all were more or less rounded, having evidently undergone attrition. The place which they occupy is not above a hundred yards square, and in this extent scarcely any other kind of stone is found, but beyond it the ground is covered in a similar manner with rounded blocks of sandstone of the same nature as that which forms the mass of the Serra. Similar deposits exist along the base of the range, but all in isolated patches, as in the present instance. I have purposely deferred till now making any remarks on the geology of the district around Crato, but I must premise that the substance of what is here stated is taken from a paper read by me before the Glasgow Philosophical Society, in April 1843, and which has since appeared in the Proceedings of that Society. Nothing like chalk, with its accompanying flints, has yet been found on the continent of North America; but in New Jersey Dr. Morton has described a deposit which he considers to be equivalent to the lower or green sand beds of that formation, and to which he has given the name of “The ferruginous sand formation of the United States.” The fossil remains which it contains prove the correctness of his opinion. As regards the South American continent, it is asserted by Humboldt, that it contains neither oolite nor chalk, from the fact that no traveller who has hitherto written on the geology of that immense continent, has ever met with either; it was therefore a source of no little satisfaction to me to find that I had been the first to discover, in the new world, the entire series of rocks which constitute the chalk formation, specimens of all of which I did not fail to collect.