THE WORK OF RUNNING WATER. 



73 



Other modes of valley development. — If as a new area of land emerges 

 from the sea its surface has a depression without an outlet, and such an 

 assumption is by no means improbable, the depression would be filled 



Fig. 54. — Diagram to show how a valley may be developing all the way from a water- 

 filled basin (lake) to the sea at the same time. Small valleys leading to the lake 

 are also developing. The black area=the sea. 



with sea-water. The inflowing water from the surrounding land might 

 fill the basin to overflowing, and the outflow, finding exit at the lowest 

 point in the rim of the basin, would flow thence toward the sea. Such a 

 stream would develop a valley, the history of which w^ould be somewhat 

 different from that which has been sketched. Instead of developing 

 headward from the sea, the valley would be in process of excavation 

 all the V7ay from the initial basin to the sea at the same time (Fig. 54). 

 The upper end of the valley might ultimately be cut to the level of the 

 bottom of the basin, when the lake would disappear. The head of the 



