PLATE 4 



EXPLANATION OF FIGURES 



Views of specimen no. 2: a, on dark mixed sand, partly covered with this material 

 (after two days); b, on white glass plate, shortly after transfer to this following 

 sojourn on dark sand; c, on coarse gravel (after two days); d, on white glass plate, 

 shortly after transfer to this, following Sojourn on coarse gravel. (Compare this 

 with b. In d, the gravel pattern has persisted to some degree, despite an immediate 

 partial disappearance of this). 



486 



