SEA-FISHERIES LABORATORY. 147 



' Manganese was found to be present in several of the 

 varieties of Oysters analysed. Its detection is readily 

 effected in the electrolytic method of analysis as it 

 separates at the anode as peroxide. Colne Oysters con- 

 tained 0*14 mgrme. per Oyster — a rather smaller quantity 

 than the iron found.' 



Mussel-beds and Mud-banks. 

 By E. L. Ascroft. 



On the Lancashire and Cheshire coasts it is often 

 noticed that Mussel-beds are situated on banks of mud. 

 Mussels require, in the earliest shelled stage, some 

 hard substance to attach themselves to, such as stone, 

 gravel, hardened sand (such as Sabellaria tubes, for 

 instance), shells, such as Cockles or Mussels, wooden 

 piles, and the bottoms of boats. As they grow up and 

 increase in size (when located where there is little wave 

 action), through their excreta and the mud settling 

 amongst them they are inconvenienced, and to escape 

 being buried a lengthening of their cables, or byssus, takes 

 place, and so they lift themselves. This process, repeated 

 time after time, raises the Mussels a great height above 

 their original location, and the bed of mud increases 

 accordingly. 



The greatest depth that I have heard of occurred in the 

 River Ribble, where a bed of gravel was bare in the 

 channel a little above Lytham, when a strike of Mussels 

 occurred on it, and in the course of three years the 

 Mussels accumulated a bank of mud ten feet in depth — 

 there being no wave action to affect it. 



At St. Annes-on-the-Sea, below the pier, there is a bed 

 of gravel on which a strike of Mussels occurs every two 

 years. During the two years growth the mud gets to a 



