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bulletin: museum of comparative zoology. 



the states of Parana and Sao Paulo. Near the town of Sao Pedro de 

 Itarare at the raihvay bridge this river flows in a channel which at one 

 point in its cross-section is not more than three feet wide. 



The channel lies in the white Devonian sandstones which present 

 no great variation from layer to layer offering opportunity for the 



Fig. 29. — Map of the Parahyba and Tiete rivers in Sao Paulo (After H. WilUams). 



selective solution which in limestone countries often produce similar 

 gorges. The bottom of this gorge is said to be between 62 and 63 

 meters below the railroad bridge. 



At one point west of the railway bridge there is a natural bridge 

 of the sandstone which evidently points to the origin of this gorge 

 as an underground stream. 



It remains to note the curious course of the Parahyba in relation to 

 the headwaters of the Rio Tiete in eastern Sao Paulo. The annexed 

 map, traced from that of Sao Paulo by Mr. Horatio Williams, late of 

 the Sao Paulo Geographical and Geological Commission, sets forth 

 the pattern of the streams. (Fig. 29,) 



It will be noted that the upper course of the Rio Parahyba under 

 the name Parahytinga follows a southwest course to the great bend 

 at Guarerema whence the course is northeastward to the sea beyond 

 the limits of the map. These courses are in essential adjustment to 

 the structure of the underlying Pre-Devonian rocks but the basin of 

 the river below the great bend is largely formed by the Tertiary non- 

 marine beds before mentioned. The great bend is made by a trans- 

 verse gorge cut through the Pre-Devonian series which rise a few 

 hundred feet above the riverplain. It is therefore to be presumed 

 that the course of the river at this point is inherited from a former 

 course which lay at the level of the intervening hill-tops. This earlier 



