AGE OF THE CATlNGA LIMESTONE 205 



The fossils found in the Catinga limestone seem to bear out this theory 

 of its age. So far as these fossils have been studied, they all belong to 

 forms now living. A few specimens found at Varzea do Sal, in the 

 Salitre Valley, were submitted to Dr. Wm. H. Dall, of the Smithsonian 

 Institution, who under date of N'ovember 8, 1909, writes as follows : 



"I have carefully examined the specimen you sent and find the land shells it 

 contains comprise at least two and possibly more species of BuUmulus of the 

 subgenus Anctus, still characteristic of the region. This subgenus is at least 

 as old as the middle Oligocene, but the species of that age, so far as I have 

 seen them, are small. Yours are much larger and probably not so old. I 

 should suspect them to be in a general way Miocene or Pliocene, but of course 

 there is no way of arriving at certainty from the fossils alone." 



At many places one finds the living shells in the process of being im- 

 bedded in the limestone now forming. 



In speaking of the older Catinga limestones, I have ventured to refer 

 them tentatively to the Miocene. I fully realize that such a reference is 

 risky from a paleontologic point of view; but, in the absence of diag- 

 nostic fossils, nothing better can be done at present. The reason for re- 

 ferring the rocks to any horizon at all lies in their stratigraphic relations 

 to the rocks about them in the evidence of a Miocene uplift of the region 

 and of a greater rainfall during that period. 



Eesume of Conclusions 



In the secondary valleys of the semi-arid limestone regions of the in- 

 terior of Bahia chemical aggradation is in progress on a large scale. 



This aggradation consists in the removal in solution of the older lime- 

 stones of the higher grounds and their deposition over the plains and in 

 the stream channels. These deposits bury up and enwrap anything that 

 happens to lie on the valley floor or in the channels of the secondary 

 streams, so that locally they contain boulders and rock fragments of 

 many kinds and plant and animal remains. Land and fresh-water shells 

 are especially abundant in these newly formed rocks in some localities. 



Over large areas the channels of the secondary streams are already 

 completely filled with these lime deposits and vegetation has encroached 

 on them until they are now covered by the ordinary forest growths. Only 

 the large perennial streams, like the Sao Francisco itself, are able to keep 

 their channels open and free from these lime deposits. 



Over broad flat surfaces of the side valleys the rain waters move the 

 lime forward year after year, taking it up on the somewhat higher 

 grounds and depositing it on the somewhat lower lands. In some places 

 the lime deposits form at and down over the faces of bluffs, which are thus 



