AN OLDER CATINGA LIMESTONE 201 



The lime rock is quarried at Carnahyba, and considerable lime is there 

 burnt in crude kilns. The limestone exposed in the pits at Carnahyba is 

 go firm and compact that the rock dresses well and even takes a good 

 polish. This rock has been extensively used by the railway officials for 

 station buildings, floors, platforms, etcetera. But even in these thick beds 

 the limestone contains sand grains and occasional water-worn pebbles. A 

 careful search was made for fossils but without success. 



North of Carnahyba station the limestone seems to underlie the plateau 

 to about kilometer 433.5. Here it seems to thin out and disappear. To 

 the north the rocks are all schists and granites until the alluvial plains of 

 the Eio Sao Francisco are reached south of Piranga. 



The accompanying section, constructed from personal observations 

 placed upon the railway profile, exhibits the structural relations and 

 geographic distribution of the limestones between Angico and Joazeiro. 



J:^ 



Xi'mtiftnt o,t nt suT/ttcc. 



Figure 1. — Profile of the Sao Francisco Railway 



From the watershed near Jaguarary to Rio Sao Francisco at Joazeiro. Reduced from 

 profile published by Doctor ArgoUo in 1898. The black area is limestone. Geology by 

 J. C. Branner. 



Eesume concerning the old Catinga Limestone along the Eailv^ay 



The characteristic features of this particular limestone deposit are as 

 follows : it is a surface deposit following the gentle slope of the land. It 

 rests unconformably on the old crystalline rocks of the region, penetrates 

 the crevices in them, and enwraps boulders and residual lumps of the 

 older rocks. Boulders are also found occasionally in any part of the beds. 

 The older rocks rise through the limestones, forming hills and mountains. 

 Where stream channels cross the limestone area, the underlying rocks are 

 uncovered, but the limestone is deposited in marly layers down the slopes, 

 especially where they are gentle. The limestone contains sand and 

 boulders, and in the same way forms about plant and animal remains. 

 The limestone is generally covered by a snuff-colored soil, and over this 

 are scattered small, rusty boulders. 



