40 ANNALS NEW YORK ACADEMY OF SCIENCES 



by massive sections (i. e., faces of mesas, etc.) of the Piano Alto. These 

 sections appear like many flat-topped sierras, but are nothing more than 

 the perpendicular faces of the remains of a dissected plateau. From a 

 distance, these sections look like gigantic modern fortresses; but as one 

 approaches nearer and nearer to them, he notes that there are immense 

 sand hills (campinas), which slope to and away from these sections of the 

 Piano Alto. That is to say, the bases of the perpendicular faces of the 

 sections are about 1000 feet below the top, while the tops of the campinas 

 which join the same bases are often not more than 500 feet lower than 

 the top of the sections. Hence the result of erosion is very striking in all 

 the region of the Piano Alto, since the original high points tend to be- 

 come the lowest. 



The explorer is impressed by the great number of the highland brejos 

 which flow along parallel lines and are about 6600 meters apart. These 

 brejos are often less than 100 feet wide and usually have a small, rapid, 

 clear stream in the center. The edges are so boggy and full of palms and 

 other typical swamp plants that one often encounters great difficulty 

 either in getting water to drink or in crossing them. 



The Brejo de Varedao appears to be due to unequal erosion and a con- 

 sequent deposition of sediment about the ends of the swamps. This region 

 offers a peculiar case of stream piracy unless Rio Sapao has cut back into 

 the headwaters of both Bio Nova and Eio Formosa. At any rate, the 

 Brejo de Varedao is gradually being drained by Eio Sapao, which is cut- 

 ting through the hard basal highland rock in its rapid descent to Bio Sao 

 Francisco on one hand and by a similar action of Bio Formosa, which 

 flows out of the opposite end of the same swamp to Bio Tocantins. Dur- 

 ing heavy rains, the Bio Nova still assists in draining this swamp. In 

 fact, it is almost impossible to ride between its headwaters and the edge 

 of the Brejo de Varedao, except during the dry season. 



It was with great difficulty that the writer pushed his way through the 

 swampy margins of the Brejo de Varedao to its lakelike central part, 

 which could not be fathomed by the longest poles obtainable. In the 

 middle, there was no current, but at the opposing ends were the rapid Bio 

 Sapao and Bio Formosa, which at once leave the swamp, flowing over the 

 basal highland formation. These streams are on the average 20 feet wide 

 and four feet deep during the rainy season. At this time the Brejo de 

 Varedao is about eight miles long and less than one mile wide at its 

 widest part. 



During the rainy season, a canoe can descend from the Brejo de Vare- 

 dao with little difficulty as far as the great cataracts of Paulo Affonso of 

 the lower Rio Sao Francisco; but a canoe cannot descend so easily from 



