196 J. C. BRANNER AGGRADED LIMESTONE PLAINS, BAHIA, BRAZIL 



been founds and we are left to conclude that the siliceous materials are 

 only residual parts of the Salitre limestones themselves. 



The Valley of Eio Jacare 



The geological history of the valley of Eio Jacare is the same, or nearly 

 the same, as that of the Salitre Yalley. It is not necessary, therefore, to 

 go into a detailed description of these same phenomena in that region. 

 It may be noted that the Catinga limestones spread from the valley of the 

 Jacare into and over a large part of the Calmon Valley. Whether these 

 are derived from the Salitre limestones that formerly partly encircled the 

 Calmon Valley, or whether they have come from the Salitre limestones 

 farther up the valley of the Jacare, is not now known. 



It is to be noted, also, in regard to the valley of the Jacare that it is a 

 long valley that heads in the mountains of the Chapada Velha. The im- 

 mediate valley of the river is a comparatively narrow channel cut in a 

 great plateau. The central portion of this plateau is made of closely 

 pressed Salitre limestones, and around this and along the Jacare is a 

 series of sediments of later date, probably of Tertiary age. On top of the 

 limestone plateau the Catinga limestones are forming, as already ex- 

 plained, filling up old river channels and extending out over the adjacent 

 sediments. Striking examples of channels being filled up with recent 

 lime rock are to be seen at Eecife, near the divide between the Jacare and 

 the Verde. In one district the Catinga limestones have been replaced by 

 silica, so that their places is taken by extensive deposits of chalcedony. 

 These chalcedony deposits are in the Eiacho Feio drainage between Gruna 

 and Jacare. 



The Valley of the Eio Verde 



The Salitre limestones of the valley of the Jacare extend right across 

 the watershed between that stream and the Eio Verde and westward to the 

 base of the Serra do Gongalves, and everywhere across the entire regioTi 

 the processes of solution and redeposition are in operation. The fillinfij of 

 old stream channels with recent limestone is noteworthy at and about 

 fazenda Gabriel. At Eecife and Gabriel, and over the wide and gentl>* 

 sloping watershed between the Jacare and the Verde, not only are th(^ 

 stream channels choked up with deposits of lime, but many of them are 

 now overgrown with forests, which spring not from the original channels, 

 but from the marly deposits that fill them. 



Climatic Eelations 



In a region as well elevated as the one under consideration we ordi- 

 narily expect to find streams deepening and widening their channels, hi 



