woodworth: geological expedition to brazil and chile. 73 



indicate, by the detailed structure of the surfaces, that the down- 

 throw Avas on the northeast side in accordance with the structure of 

 the Orleans basin. It is evident therefore that repetitive small faults 

 occasion the base of the Permian section in this district. 



The conglomerates are exposed along the ri\"er banks below the 



i- £- i, V/.^,V/, ^7<-?<> 



Fifi. 21. — Section of beds in Orleans basin, south bank of the Rio Tuberao. 

 Tlie rock on west is a broad trap dike. 



town and are best shoAvn on the north bank under the railroad track, 

 (Fig. 22). There is here a water laid conglomerate mainly of granite 

 pebbles with a few quartzite and quartz pebbles. The conglomerate 

 is overlain by cross-bedded grits, the cross-bedding dipping to the 

 north and northwest as if deposited by currents of water flowing at 

 least locally in that direction. The pebbles in the conglomerate bed, 

 mostly three inches in diameter, sometimes attain five inches, and are 

 embedded in a paste of granitic detritus. The subrounded shape of 

 the pebbles indicates no distant journey and their hthological character 

 betokens a deri\ation from the granitic terrane which immediately 

 underlies the local Permian section. (See Plate 25.) 



Another exposure of the conglomerate about 90 meters down stream 

 from the preceding exposure presents the cross-section of a north- 

 south ridge of coarse pebbles 

 enveloped in cross-bedded 

 sandstones. In a layer of 

 conglomerate \-arying from 

 to 60 cm. in thickness the 

 cobbles attain a diameter of 

 20 cm. The ridge-like de- 

 posit, so suggestive of a 

 buried esker, is apparently continued across the river on the south 

 bank of which there is a ridge-like exposure of conglomerate also 

 covered by sandstones. A few vards east of the ridge on the 

 north bank there is exposed a bed with rounded granite pebbles 

 scattered through a sandstone matrix as if dropped by floating ice. 



Fig. 22. — Esker-like ridge of conglomerate 

 in lower Permian beds; near Orleans. Sta. 

 Catharina. 



