180 THEORY OF THE EARTH. 



had been produced by the effects of human la- 

 bours ; and the historians who have recorded this 

 remarkable fact only differ from each other in some 

 of the more minute details. The tendency of the 

 river to flow in the new channels, which had been 

 opened for the more ready discharge of its waters 

 when in flood, continually increased; owing to 

 which the two ancient chief branches, the Voaho 

 and Prtmaro, rapidly decreased, and were reduced 

 in less than a century to their present comparative- 

 ly insignificant size; while the main direction of 

 the river was established between the mouth of 

 the Adige to the north, and what is now called 

 Porto di Goro on the south. The two before-men- 

 tioned canals of Mazzorno and 7W, becoming in- 

 sufficient for the discharge, others were dug ; and 

 the principal mouth, called Bocco Tramontane or 

 the northern mouth, having approached the mouth 

 of the Adige, the Venetians became alarmed in 

 1 604 ; when they excavated a new canal of dis- 

 charge, named Taglio de Porto Viro, or Po delle For- 

 naci, by which means the Bocco Maestro, was divert- 

 ed from the Adige towards the south. 



During four centuries, from the end of the 

 twelfth to that of the sixteenth, the alluvial forma- 

 \ ions of the Po gained considerably upon the sea. 

 The northern mouth, which had usurped the situ- 

 ation of the Mazzarno canal, becoming the Ramo di 

 Tramontane^ had advanced in 1600 to the distance 



