95 



on the northern sides the two hilly groupes, 

 known by the names of la Vega de San Juan, and 

 of Macanao. The Laguna grande of Margaretta 

 has a very narrow opening toward the south, and 

 small boats pass arastrados, that is by a portage, 

 over the neck of land or northern dyke. Though 

 the waters on these shores seem at present to 

 recede from the continent, it is notwithstanding 

 very probable, that in the lapse of ages, either 

 by an earthquake, or by a sudden intumescence 

 of the ocean, the long island of Margaretta 

 will be divided into two rocky islands of a tra- 

 pezoidal form. 



On climbing up the Cerro del Barigon, we 

 repeated the experiments made at the Oroonoko, 

 on the difference of temperature of the air and 

 the decomposed rock. The temperature of the 

 former was only 27° cent., toward eleven in the 

 morning, on account of the effect of the breeze ; 

 while that of the latter rose to 49* 6°. The 

 sap that rises in the candelabra cactuses (cactus 

 quadrangularis) was from 38° to 41°. This 

 beat was shown by a thermometer, the ball of 

 which I placed within the fleshy and succulent 

 stem of the cactus. This interior temperature 

 of a plant is composed of that of the sand in 

 which it's roots are fixed, and that of the ex- 

 ternal air modified by the state of the surface 

 of the stem exposed to the rays of the Sun, it's 

 evaporation, and the conducting power of the 



