NOTES ON BRAZIL. 441 



more intimately miscible, has been separated and carried by the stream 

 to a lower station. These sandy spots sometimes contained rounded 

 pebbles, but were more commonly seen without them, and, in one 

 instance, where the stream had cut deeply into the earth, confused strata 

 of vegetable soil, clay, sand of different kinds and colours, and even of 

 peat, were exposed to view. 



In our progress to-day we passed and examined, in a cursory way, 

 one of the largest of those chasms which, in Brazil, are knowai by the 

 name of Corgo. Something like them occasionally occurs, on a small 

 scale, in some of the chalky and peaty districts of our own country. 

 They are excavations in the side of a hill, a sort of pit, open at one end, 

 with very rough unformed sides, destitute of verdure, and having their 

 longest line nearly at right angles to the ridge of the hill on whose side 

 they appear. They are formed at first by the junction of very little 

 streamlets, which acquire momentum enough to tear away the soil. In 

 subsequent rains the water shoots, with accumulated force, over the 

 brink, falls upon the ruin already produced, and enlarges it ; a similar 

 process goes on until the chasm becomes frequently many hundred feet 

 in length, sometimes two or three in breadth, and often more than one 

 hundred deep. In this state the sides are continually crumbling in ; 

 rain washes them down, and the wreck is borne away by the solvent 

 power and the force of the accumulated waters, until, in process of time, 

 the sides acquire a regular slope, the bottom is covered with the feldspar 

 and other heavy materials w'hich existed in the clay, and thus a steep dell 

 and at length a valley is formed, and lastly grass grows upon its sides. 



I have observed many instances where these Corgos have owed their 



origin to what may be called, perhaps, a less natural process. During 



the dry season Ants and Armadillos, both of which may be numbered 



among the pests of the country, burrow into the sides of the hills. In the 



rainy season water descends into these holes, and, uniting with the clay, 



becomes a puddle ; if the pressure of the mass be sufficient to burst its 



way through the soil, a Corgo is begun, the growth of which will be 



determined by the form of the upper ground, the solidity of the materials, 



3 K 



