Lisboa — Permian Geology of Northern Brazil. 437 



rina system. These sediments extend from Alpercatas to 

 Grajahu. 



The Corda sandstone. — The Corda sandstone is greatly 

 developed in the upper Mearim and also in its tributary. 



In that region a large number of small, reel, table-topped 

 hills are scattered about in the extensive plains which form 

 the terraces of the channels of these two rivers. They are 

 here isolated, here in alignment, or perhaps bunched together 

 in a sort of labyrinth, separated by uniform channels planed 

 down, with regular slopes, in some places winding, and called 

 boqueiroes by the inhabitants. These give the region a char- 

 acteristic physiographic appearance. 



The sediments are uniformly sandy and red except at the 

 contact or near the flows of the eruptives. Between the 

 Corda and Alpercatas rivers, at Manoel Theodoro, the red 

 sandstone becomes quartzitic. In the high divides there are 

 eruptions of trap. 



The thickness of this sandstone of Corda is at least 100 

 meters. At Grajahu a bed of coarse conglomerate with flint 

 covers a flow of eruptive rock which forms an extensive sheet 

 on top of the red sandstone. In the Serra Yermelha this bed 

 seems to be covered by a red sandstone. 



The Serra Vermelha is made up of the front wall of the 

 plateau in the marginal plain of the Grajahu above the city of 

 that name. Here it can be seen that the beds clip locally in a 

 west-northwest direction. The thickness of the red sandstone 

 beds and the included trap is 235 meters. On this sandstone 

 there lies unconformably a yellow, friable sandstone which 

 was included in the upper series of Cretaceous sediments. 



The Grajahu Series (Cretaceous). 



The Crajahii series is quite thin. It is composed of two 

 types of sediments, a yellow friable sandstone covered by a 

 quartzitic sandstone, with silicified trunks of dicotyledons. It 

 forms the top of the plateau of Grajahu. 



The Cretaceous of the interior seems to extend uninter- 

 ruptedly to the coast, the sediments being argillaceous in some 

 places and sandy and friable in others. At Carutapera in the 

 extreme northwest of Maranhao 1 observed a fossiliferous 

 limestone with a fauna similar to that of Piabas. This shows 

 therefore the existence of marine Cretaceous basins on the 

 coast of Maranhao. 



Other Sediments. 



Certain sediments were observed under such conditions that 

 it is difficult to locate them in the geologic column of the 

 region. Among these is a series containing bituminous shales 



