Chap. I] 



THE FORMATIONS 



187 



Sand, and gradually humus, accumulates round these groups of plants, 

 so that in time they form the centre of little sandy hillocks, termed 

 ' touradons,' only about a decimeter high. 



The touradons, thanks to the matting of the roots and stolons, already 

 possess considerable powers of resistance and can withstand even the 

 winter floods. Every year they increase in breadth, so that after a few 

 years they attain a diameter of one to two meters and already support 

 about twenty species of halophytes, among others Inula crithmoides, species 

 of J uncus, Statice, Plantago, and several grasses. Slowly, continually 



Fig. ioi. From the Camargue. Horizontal sandy flats liable to be flooded by storm-tides, with the 

 earliest vegetation of Salicornia macrostachya. After Flahault and Combres. 



struggling against the floods, the touradons gradually raise the soil, 

 whilst the rain continually sweetens them and renders them suitable for 

 the growth of non-halophytes. 



The dunes in the Camargue are also very instructive. In some parts 

 of the coast they form parallel ridges separated, valley-like, by the 

 originally flooded tract with its touradons. Their vegetation constantly 

 increases inland. Evidently there was once a general upheaval of the 

 ground ; and dunes as well as touradons have remained as geological 

 survivals. The succession of the dunes exhibits all intermediate stages, 

 from the commencement of vegetation on the outermost dunes to the 



