194 J. C. BRANNEK AGGRADED LIMESTONE PLAINS, BAHIA, BRAZIL 



Through some of these depressions the water flows off promptly, but in 

 most of them it stands for a time in broad shallow pools. In such places 

 the waters bring in lime from the higher grounds, to be precipitated on 

 exposure in the warm shallow waters or on complete evaporation. These 

 low grounds are everywhere covered with the characteristic soft deposits 

 of lime, showing that it is precipitated from solution.^ The fresh deposits 

 in these places are all soft and marly, but the old ones are as hard as any 

 limestone ever gets to be. At many places these lime deposits, both the 

 newer and older ones, contain plant impressions and inclose the remains 

 of land shells. At one place on fazenda Varzea do Sal large numbers of 

 these shells were found cemented together, forming a hard rock. So far 

 as has been observed, the shells are forms now living on the ground. ( See 

 plate 15, figure 1.) 



The process seems to explain the presence of both angular fragments 

 and water-worn boulders of all kinds of rocks in the Catinga limestones 

 wherever they are found. 



An impressive modification of these deposits forms where the topog- 

 raphy is favorable. Where a broad, gentle, and rather even slope carries 

 the lime-charged waters in shallow sheets toward a channel, the lime is pre- 

 cipitated more rapidly along the edge of the plain, where, on account of a 

 change to a steeper grade, the water breaks into ripples or spray. This 

 causes the bluff to encroach steadily on the low ground, and the process 

 must eventually lead to the low ground being entirely filled up. The accom- 

 panying photograph (plate 16, figure 2) shows one of these limestone 

 bluffs encroaching on a narrow valley that drains into the Salitre Eiver 

 a few miles north of fazenda Salitre. The top of the cliff curves over 

 like the surface of one of the travertine stream barriers. The bluff is full 

 of caverns, produced by the irregularity of the deposit, and the roofs of 

 the cavern are hung with stalactites. Often the travertine is deposited in 

 masses of such shapes that they break from their own weight and form a 

 talus slope at the base of the bluff, and this, too, in time is covered over 

 by later deposits and is incorporated in the great limestone sheet. 



Similar cavernous bluffs are found at many other places along these 

 limestone valleys. Mr. H. E. Williams, who visited the locality at my 

 request, sends me the following notes in regard to the one just below the 

 falls of Eio Salitre, some 50 kilometers southwest of Joazeiro : 



"At the Tocas, just below the Caxoeira, there is a beautiful limestone bluff 

 from twenty-five to thirty meters high overhanging and full of holes and 



8 An Interesting accompanying phenomenon is the distribution of recent iron deposits 

 along the bases of the hiUs. This appears to be due to the more prompt precipitation of 

 iron where the waters flow from the slopes. 



