Waring: Geology of Northeastern Brazil. 195 



appears, that, since the gorge was cut, there has been some depression 

 of the ridge. Soundings' made in the gorge in connection with studies 

 for a dam show bedrock to be nine to fourteen meters below the 

 surface of the pool, in which the water is normally two or three meters 

 deep. Similar conditions exist where the Rios Pianco, Aguiar, and 

 Piranhas cross Serra de Santa Catharina, and this range seems also 

 to have undergone subsidence, presumably due to faulting since the 

 streams cut their channels across it. 



Crushed gneiss with steep south dip continues southwestward from 

 Lavras. i\bout ten kilometers from this town a band of darker, more 

 schistose rock, three hundred or four hundred meters wide, was 

 crossed, and then a schist or altered shale, with bedding or cleavage 

 planes striking southwest and with vertical dip. This rock continues 

 southwest along Riacho do Meio for a few kilometers, and then 

 seems to be overlaid by red sandstone. This latter is presumably an 

 outlier of a basal portion of the Cretaceous rocks which compose 

 Chapada do Araripe, to the south." Near Ema a band a few meters 

 wide of chloritic (?) schist was seen. It is perhaps a contact meta- 

 morphic rock along the border of a zone of dioritic or granitic rock, 

 which extends southward from that point. 



Gneiss again appears at Junco, and it forms the Serra de Santa 

 Maria a few kilometers to the south, the dip being steeply southward. 

 Gneiss also forms the hills between the serras of Santa Maria and 

 Sao Pedro and constitutes the core of the latter range. 



Small^^ found that between Iguatu and Sao Pedro the gneiss has a 

 remarkably constant steep south dip; but that thence northwestward 

 to the vicinity of Taua and Cratheiis and thence eastward to Boa 

 Viagem the gneiss is so crushed and crumpled that its structure is 

 not clearly evident, though the dip seems in the main to be steeply 

 to the north or northwest. 



About three kilometers southwest of Sao Pedro, which is at the 

 summit of the range, altered shale appears and continues down the 

 slope to the channel of a small stream ten kilometers from Sao Pedro. 

 The hills thence to the southwest are in part covered with cherty 

 material for two or three kilometers and then the red sandstone of 

 Chapada do Araripe begins. 



11 The succession of materials composing this highland have been described by 

 Crandall (Publ. No. 4 of the Inspectoria, pp. 27-28); and by Small (Publ. No. 25 

 of the Inspectoria, pp. 25-36). 



1- Publ. No. 25 of the Inspectoria, p. 40. 



