60 



river owes this immense advantage to the con- 

 stant direction of it's course. It flows from 

 west to east in a vast plain, that forms a longi- 

 tudinal valley, between the mountains of Parima 

 and the great mass of the mountains of Brazil. 



I was surprised to find by actual measure- 

 ments, that the rapids of the Oroonoko, the tur- 

 bulent noise of which is heard at the distance 

 of more than a league, and which are so emi- 

 nently picturesque from the varied appearance 

 of the waters, the palm trees, and the rocks, have 

 not probably, on their whole length, a height of 

 more than twenty-eight feet perpendicular. In 

 reflecting on this, we find that it is a great deal 

 for rapids, while it would be very little for a 

 single cataract. The Yellalas of the Rio Congo, 

 in the contracted part of the river from Banza 

 Noki as far as Banza Inga, furnish, between the 

 upper and lower levels, a much more considera- 

 ble difference ; but Mr. Barrow observes, that 

 among the great number of these rapids there 

 is one fall, which alone is thirty feet high. On 

 the other hand, the famous pongos of the river 

 Amazon, so dangerous to go up, the falls of 

 Rentema, of Escurrebragas, and of Mayasi, have 

 but a few feet of perpendicular height. They 

 who are engaged in hydraulic works know the 

 effect, that a bar of eighteen or twenty inches 

 high produces in a great river. The whirling 

 and tumultuous movement of the water does 



