106 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
the states of Parand and Sao Paulo. Near the town of Sao Pedro de 
Itararé at the railway 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 
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RO. pan 
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Fia. 29.— Map of the Parahyba and Tieté rivers in Sio Paulo (After H. Williams). 
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 Tieté 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 
