515 



forces ; but we must remark, that the dip at 

 Caraccas is much greater than could be sup- 

 posed from the situation of the town, and that 

 the magnetical phenomena are modified by the 

 proximity of certain rocks *, which constitute so 

 many particular centres, or little systems of at- 

 traction. 



* I have seen fragments of quartz traversed by parallel 

 bands of magnetic iron, carried into the valley of Caraccas 

 by the waters descending from the Gallipano and the Cerro 

 de Avila. This banded magnetic iron ore is found also in 

 the Sierra Nevada of Merida. Between the two peaks of 

 the Silla angular fragments of cellular quartz are found, 

 covered with red oxide of iron. They do not act on the 

 needle. This oxide is of a cinnabar red colour. 



2l2 



