384 ORVILLE A. DERBY 



on the northern side of the river, and the base of the sandstone is 

 seen to consist, for a thickness of a few meters, of a coarse con- 

 glomerate containing pebbles and bowlders of gneiss and granite. 

 At one point the conglomerate is seen to rest on granite. The road 

 then ascends, over a chert-strewn trail, a table-topped ridge known 

 as the Serra das Araras, which is said to abut on the river in a fine 

 limestone bluff. On the top of this ridge the aneroid indicated an 

 elevation of 575"^. Small outcrops of limestone occur on the western 

 descent to the river Una, where just below the bridge is another 

 limestone bluff 35"^ high. The beds here, as at Bebedouro, have a 

 slight westerly dip of 5-10°. On the ascent from the river Una the 

 road passes over about 100™ of strata above the limestone, but no 

 rock in situ appears. Cherty nodules appear in three distinct zones,, 

 and the underlying rocks are presumed to be shales and sandstones 

 with intercallations of limestone. 



A diligent search for fossils both at Bebedouro and Rio Una was 

 fruitless, although the limestone seems very favorable for preserving 

 them. Limestone is reported to occur near the head of the Rio Una, 

 and the valley of this small river is presumed to be almost exclusively 

 occupied by this series, which also appears to the northward of the 

 Paraguassu in the valley of the lower Santo Antonio, and Utinga 

 in the neighborhood of Pegas. So far as could be made out, this 

 series is from 200 to 250"^ thick, and is practically undisturbed, or 

 at all events much less so than the strata in the adjacent Serra 

 do Espinhafo zone. About a quarter of the thickness, and perhaps 

 much more, is composed of limestone which is characteristically 

 cherty, at least in many of its layers. 



From Mocambo to Passagem the road passes, at an elevation of 

 600™, over a ridge that rises considerably higher to the southward. 

 The rather unsatisfactory rock exposures consist of sandstone, in 

 places lying horizontally, in others with a moderate dip to the east- 

 ward or to the westward. The section along the road seems to be 

 across the expiring end of a fold which to the southward forms a 

 high ridge known as the Serra do Sincora, on the eastern margin of 

 the Serra do Espinhafo plateau. An appearance, as seen from a 

 distance, of synclinal structure in the valley of the Piabas, on the 

 western flank of the supposed fold, confirms this interpretation. 



