MARINE BIOLOGICAL STATION AT PORT ERIN. 47 



new and somewliat unusual appearance on the sand about 

 or a little above half-tide mark. The hollows of the 

 ripple-marks and other slight depressions formed by the 

 water draining off the beach were occupied or outlined by 

 a greenish-brown deposit which in places extended on to 

 the level parts so as to discolour patches of the sand (see 

 fig. 22). 



Fig. 22. The general appearance of the brown deposits in the ripple-marks 

 on the sand, reduced in size. 



" In this position the deposit remained, more or less, 

 for a month — waxing and waning, sometimes increasing 

 in a tide, say, roughly tenfold, and at other times 

 apparently disappearing for a day or two and then 

 re-appearing either on the same part of the beach, or it 

 might be a few hundred yards away. At one time it 

 discoloured a continuous stretch of sand about fifty yards 

 long by five yards in breadth a little below high-water 

 mark, and was noticeable from some distance away. 



" On first noticing it I supposed the appearance was 

 caused by a deposit of Diatoms, but on taking a sample 

 to the laboratory, microscopic examination showed 

 that although a few Diatoms (including Navicnla 

 amphisbaena, or a closely allied form) were present, the 



