Immense tracts of flat bare rock form peculiar and characteristic features in the Deserts both of Africa and Asia. In the Schamo, which separates Mongolia and the mountain chains of Ulangom and Malakha-Oola from the north-west part of China, these banks of rock are called Tsy. They are also found in the forest-covered plains of the Orinoco, surrounded by the most luxuriant vegetation (Relation Hist. t. ii. p. 279). In the middle of these flat tabular masses of granite and syenite of some thousand feet diameter, denuded of all vegetation save a few scantily distributed lichens, we find small islands of soil, covered with low and always flowering plants which give them the appearance of little gardens. The monks of the Upper Orinoco regard these bare and perfectly level surfaces of rock, when they are of considerable extent, as peculiarly apt to cause fevers and other illnesses. Several missionary villages have been deserted or removed elsewhere in consequence of this opinion, which is very widely diffused. Supposing the opinion correct, is such an influence of these flat rocks or laxas to be attributed to a chemical action on the atmosphere, or merely to the effect of increased radiation? [5] p. 2.--“_The Llanos and Pampas of South America, and the Prairies of the Missouri._” The physical and geognostical views entertained respecting the western part of North America have been rectified in many respects by the adventurous journey of Major Long, the excellent writings of his companion Edwin James, and more especially by the comprehensive observations of Captain Frémont. These, and all other recent accounts, now place in a clear light what, in my work on New Spain, I could only put forward as conjecture, on the subject of the mountain ridges and plains to the north. In the description of nature as well as in historical inquiries, facts long remain isolated, until by laborious investigation they are brought into connection with each other.