ANNOTATIONS AND ADDITIONS. 49 



feet) lower. Farther to the west, near the junction of the Caura 

 with the Orinoco, and to the east of the mission of S. Pedro de 

 Alcantara, an extensive tract of dense forest sank down in an earth - 

 quake in 1.790, and a lake was formed of more than 300 toises 

 (1918 English feet) diameter. The tall trees (Desmanthus, Hy- 

 menaeas, and Malpighias) long retained their foliage and verdure 

 under the water. 



( 3 ) p. 26. " We seem to see before us a shoreless ocean." 

 The prospect of the distant Steppe is still more striking, when 

 the spectator has been long accustomed in the dense forests both to 

 a very restricted field of view, and to the aspect of a rich and highly 

 luxuriant vegetation. Ineffaceable is the impression which I received 

 on our return from the Upper Orinoco, when, from the Hato del 

 Capuchino, on a mountain opposite to the mouth of the Rio Apure, 

 we first saw again the distant Steppe. The sun had just set; the 

 Steppe appeared to rise like a hemisphere; and the light of the 

 rising stars was refracted in the lowest stratum of air. The exces- 

 sive heating of the plain by the vertical rays of the sun causes the 

 variations of refraction occasioned by the effects of radiation, of 

 the ascending current, and of the contact of strata of air of unequal 

 density to continue through the entire night. 



( 4 ) p, 26." The stony crust." 



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, de- 

 nuded 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 

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