668 ROLLIN T. CHAMBERLIN 



particulars by what was seen during the second visit. Its essen- 

 tials are here recalled for the sake of the discussion following. 



i. During a submergence of this portion of the east coast of 

 Florida there was laid down a striking marine shell marl which has 

 sometimes been called "coquina." It is the oldest formation 

 exposed to view and has been referred without question to the 

 Pleistocene. Though its precise place within the Pleistocene has 

 not been determined, its fauna was essentially the same as that 

 now living in the adjacent ocean. Following the deposition of the 

 marine shell marl, a withdrawal of the sea gradually brought this 

 region into the horizon of terrestrial action. In the transition, 

 beach conditions prevailed, resulting in sandy deposits, partly 

 marine, partly terrestrial. 



2. At the appropriate stage in the withdrawal of the sea a 

 barrier ridge was developed immediately to the west of the present 

 location of the Florida East Coast Railway. This ridge parallels 

 the railroad and the coast for many miles both north and south of 

 Vero, and throughout most of its extent it is a pronounced topo- 

 graphic feature. West of it was a marshy area. 



3. With further withdrawal of the sea a newer barrier ridge 

 developed from two to two and one-half miles east of the earlier 

 Vero beach ridge. This constitutes the present east coast of 

 Florida. For over one hundred miles it incloses, between itself 

 and the mainland, a salt-water lagoon, known as the Indian 

 River. 



4. After the withdrawal of the sea from the Vero beach ridge, 

 erosion developed a channel in essentially the position now occupied 

 by Van Valkenburg's Creek. The very low gradient and notable 

 width of this channel in proportion to its very insignificant depth, 

 which was limited by sea-level, suggest that erosion, which here was 

 slow at the best, was in progress for a considerable time. 



5. In the marshy region west of the Vero beach ridge bog 

 deposits accumulated here and there. Cementation had also 

 affected certain horizons of the sands of this tract and had con- 

 verted them into a sandstone. This had been effected by the depo- 

 sition of iron and manganese oxides as well as organic matter in 

 the sands. The length of time involved in this process of conver- 



