EIVERS OF GUIANA. 15 



the Potaro is precipitated over an abrupt cliff 741 feet high, and at flood water 

 the fall is 370 feet wide, decreasing at lo,v water to rather less than half that 

 width. During the rainy season Mr. iin Thurn compares the spectacle to a 

 vast curtain of water nearly 400 feet wide rolling over the top of the cliff, and 

 retaining its full width until it crashes into the boiling water of the pool which 

 tills the whole space below ; but of the pool itself only the outer margin is visible, 

 the greater part being ceaselessly tossed and hurled up in a great and high mass 

 of surf, foam, and spray. The floor of the amphitheatre over which the Potaro 

 tumbles " is occupied by a waste of fallen rocks, made black by constant moisture, 

 but capped with short, intensely green grass, except round the dark stormy pool, 

 where the rocks are entirely bare, slippery, and black. Immediately behind the 

 fall a huge dark cave is visible in the cliff, the upper edge of the cHff serving as 

 a horizon to the whole scene when viewed from below." * 



Lower down the Potaro continues still to descend as from step to step through 

 a series of romantic cascades. Formerly the great fall, at that time over 1,000 

 feet high, stood some 15 miles farther down ; but by incessantly eating away the 

 sandstone plateau over which it is hurled down to the plain, it has gradually 

 retreated while diminishing in heij^ht. The cornice of rocks from which the river 

 is precipitated consists of a hard conglomerate overlying a more friable sandstone. 

 This sandstone is incessantly eroded by the seething waters of the pool, detaching 

 huge blocks from time to time, and excavating a dark recess beneath the over- 

 hanging edge of the plateau. At sunset myriads of swallows, gathering from the 

 surrounding woodlands, sweep the precipice, dart like a flash into the misty spray, 

 and then reappear at the mouth of the cave. Such is the rapidity of their flight 

 that " their wings produce a hissing noise, which is not the least curious pheno- 

 menon of this wonderful place. After descending straight down they settle for 

 the night on the face of the cliff, by and behind the fall." f 



The Mazaruni and Lower Essequibo. 



Below the Potaro affluent the Essequibo is almost doubled in volume by the 

 contributions of the Mazaruni, which is itself joined by the Cuyuni eight miles 

 above their common mouth on the left bank of the mainstream. Pising on the 

 highest slopes of the Pacaraima Mountains, where it receives the streams tumbling 

 from Roraima, the Mazaruni is of all the Guiana rivers the most obstructed by 

 cataracts. The falls and rapids occur especially in the lower part of its course, 

 so that, despite its great volume, this river is almost entirely closed to navigation. 



At the falls of Chichi, that is, the " Sun," in the Macusi language, the fluvial 

 bed descends a total height of 890 feet (1,380 to 490) in a space of about eight 

 miles. The last obstructions occur at the so-called " Monkey Jump," some 15 

 miles above the point where the Mazaruni is joined by the Cuyuni. 



Below the confluence of the Mazaruni, the Essequibo expands into a broad 

 estuary, which attains a width of no less than 15 miles where it enters the sea. 



* Amonj the Indiani of Guiana,^. 66. 

 t lb. 



