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JENKINS— GEOLOGY OF THE 



[May 29, 



ing iinconformably on top. This unconformable contact is dis- 

 tinctly marked at these quarries and was carefully studied ; photo- 



FiG. 6. An exposure along Rio Potengy showing the contact between the 

 horizontal, fossiliferous limestones and the granites. Looking south, near 

 Alvaredo, Rio Grande do Norte. 



graphs were taken and material collected. At the point of contact 

 the sandstone is very black, probably carrying manganese. Above 

 this the sandstone has a soft white character, while on top lie the 



Fig. 7. Diagram made from a photograph of the unconformity between the 

 fossiliferous limestones and the sandstone and clay series as exposed in a quarry 

 at Jacoca, five kilometers southwest of Ceara-Mirim, Rio Grande do Norte. 



red iron-stained rocks so common over the country. On the surface 

 of the ground are loose boulders of the iron-rock. The bedding 

 of the sandstone is not very clear, as in most localities, but has 

 the general appearance of being horizontal. 



