CRETACEOUS AND CATINGA LIMESTONES 191 



The analysis shows the rock to be a very pure limestone — much purer 

 than the average.* 



The character of the bedding and the composition of the rocks suggest 

 that these limestones were deposited in rather shallow waters far from a 

 shore. The absence of false bedding suggests that the waters were not 

 commonly affected by considerable currents, and Doctor Rothpletz's sug- 

 gestion is that they are of marine rather than fresh-water origin. 



The Cretaceous Limestones 



The gray and cream colored limestones of the Sergipe series are only 

 locally developed in the State of Bahia. So far as is now known, they are 

 confined to the coastal belt in the Eeconcavo, near the city of Bahia. The 

 rocks of the Sergipe series are shown by their fossils to be of Cretaceous 

 age^ and of marine origin. Inasmuch as the limestones of this series are 

 not known to occur in the region of the limsetone plains, nothing further 

 need be said of them here. 



The Catinga Limestones 



The Catinga limestones are of recent date and are now in process of 

 formation. It will be seen, however, that the agencies that are making 

 and unmaking these rocks have long been in operation on a large scale, 

 and it is to be expected that the oldest limestones of this kind therefore 

 date back to the time when these agencies became active, while the newest 

 ones are now in process of formation. 



Salitre Valley 



The general process of the formation of the Catinga limestones and 

 the resulting aggradation will be understood from a brief description of 

 their making and unmaking in the Salitre Valley. 



Structurally the Salitre Valley is a great syncline. At its southern end 

 it is bordered by the Serra de Tombador, a range formed by the outcrop- 

 ping of the nearly horizontal Tombador sandstones.*^ This Tombador 

 series, although it is not everywhere visible, follows along the east side of 

 the valley to Sargento, where it crosses the river, forming the Cachoeira 

 do Salitre. On the west side the valley is bordered by a series of moun- 



* See Clark's composite analysis of 345 limestones. Bull. 330, U. S. Geological Survey, 

 p. 27. 



5 C. A. White : Contribuigoes & paleontologia do Brazil. Archivos do Mnseu Nacional 

 VII, Rio, 1887. 



• The geology of the Tombador range is described in Amer. Jour. Sci., vol. xxx, Novem- 

 ber, 1910, pp. 835-343. 



