404 J. BARRELL RECOGXITIOX OF ANCIENT DELTA DEPOSITS 



porarily these commou ancient conditions. The Iloang Ho, now push- 

 ing out rapidly into the Gulf of Pe-Che-Lee, faces a water body less than 

 40 meters deep. The Terek, loaded with waste from the Caucasus, is 

 building into the Caspian in waters less than 20 meters deep. The 

 Jaxartes and the Oxus are rapidly filling the Aral Sea, a shallow rem- 

 nant of the recently large interior Eurasian Sea. In all of these the 

 shore face is 5 meters or even less in depth, and a highly irregular shore 

 line testifies to the dominance of the river over the weakened wave 

 action. In the more protected parts of the shoreline the water shallows 

 without a definite boundary, but there is an absence of lagoons behind 

 barrier beaches. 



Another excellent example which illustrates conditions of waste-bear- 

 ing rivers pouring into very shallow waters is seen within the central 

 Andes, in Lake Titicaca, for details concerning which the writer has had 

 the advantage of personal discussion with Prof. Isaiah Bowman.* This 

 body of water is 100 miles long by 30 broad and in the central part 

 ranges from 350 to 900 feet in depth. f But at the two ends of the lake 

 are broad areas averaging from 15 to 30 feet in depth. The Bay of Puno 

 at one end and Lago Pequeno at the other are so nearly isolated that the 

 maintenance of such shallow water in them can not be ascribed to wave 

 action from the open lake, especially as rivers bearing a moderate amount 

 of alluvium flow into these bays. The striking feature about the shore 

 of Titicaca is the meagerness of shore erosion in general and its com- 

 plete absence on much of the shores which face these broad shallow 

 waters. Here, where the old alluvial plains slope under water, a belt of 

 clear quiet water is succeeded at a depth of several feet by a broad thick 

 belt of water g]"asses, within which, during the seasons when the land 

 pasturage is scant, the cattle revel like amphibious creatures. 



The grasses grow only on shallows which are ]iej'manently covered by 

 water and protected froui heavy wave action. On the northwest shore 

 they are found facing the open lake only where protected by the shallow 

 water of the drowned delta plain of the Suchis Eiver. Thus from the 

 evidence of Titicaca it is seen that facing shallow bottoms subaqueous 

 vegetation, at least in fresh waters, may effectively hold river muds from 

 attack by waves. 



Even where water grass does not protect the shore the waves, where 

 the adjacent bottom consists of broad shallows, show but little power of 

 erosion, for the road along which the prehistoric builders of Tiahuanaco 



* See a forthcoming paper by him on Lake Titicaca and the ruins of Tiahuanaco. 

 t For map see Geographical Journal, vol. 37, 1910, map on p. 512. See text on pp. 

 398-404. 



