180 



DYNAMICAL GEOLOGY. 



it, and show the fact of this reenforcement of the streams in the depth of 

 the valleys. 



Finally, in Tahiti, as is shown in the map below, the work of erosion is in 

 a sense completed, in spite of the general covering of vegetation. The few 

 great valleys, which here take the place of the many of the early stages of 

 erosion, extend to the coast ; and these valleys, instead of narrowing to the 



161. 





Map of Tahiti, the coral reefs excluded; the lower Bide is tlie northern, or that toward the equator: 

 PP, village of Papenoo; M, of Matavai; P, of Papaua; T, of Toanoa; P', of Papieti, the largest; P", of 

 Punaavia. The valleys are named from the villages on the coast at their termination. Wilkes' Exploring 

 Expedition Report. 



summit, widen out and stop off abruptly under precipices of at least 3000 

 feet. Some widen at their head into great amphitheaters or circs (the 

 "cirques" of French authors), illustrating well the origin of such amphi- 

 theaters. 



In the above examples, the rains and mists of the higher and cooler 



