578 



inclination of the strata. This direction of 

 the strata is independent of that of the bands 

 of formations, or their visible limits at the sur- 

 face of the soil; the lines $ and s sometimes 

 cross each other, even when one of them coin- 

 cides with «, or with the direction of the longitu- 

 dinal axis of the whole €hain. The relief of a 

 country cannot be explained with precision on 

 a map, nor can the most erroneous opinions 

 on the place and superposition of soils be 

 avoided, if we do not seize with clearness the 

 relations of the directing lines which we have 

 just mentioned. 



In that part of South America which makes 

 the principal object of this memoir, and which 

 is bounded by the river Amazon on the south, 

 and on the west by the meridian of the snowy 

 mountains (Sierra Nevada) of Merida, the dif- 

 ferent bands or zones of formations }j are sensi- 

 bly parallel with the longitudinal axis a of the 

 chains of mountains, basins, or interposed 

 plains. It may be said in general that the gra- 

 mme zone, (uniting under that denomination 

 the rocks of granite, gneiss, and mica-slate) 

 follows the direction of the Cordillera of the 

 shore of Venezuela, and belongs exclusively to 

 that Cordillera and the groupe of the moun- 

 tains of Parime ; since it no where pierces the 

 secondary and tertiary soils in the Llanos or 

 basin of the Lower Oroonoko. It thence re- 



