430 transactions liverpool biological society. 

 Hydrographical Eeadings. 



Some 60 hydrometer readings were taken between 

 October 31st and November 27th, bnt as seven stations 

 were tested, tbe actual number of readings per station 

 proved too few to establish anything but the very broadest 

 generalisations. 



During the four weeks of observations the climatic 

 conditions varied greatly, particularly with regard to the 

 quantitative distribution of rainfall. The funnel-like 

 shape of the estuary is to some extent broken by the 

 northward projecting mass of marsh, sand, &c, capped 

 by Twyne Bach. This projection may cause some con- 

 siderable ponding and less direct circulation in the South 

 of the area (see map for position of larger cockle bed). 

 The northern portion of the estuary, i.e., the major 

 river area appears to have strongly marked ebb and flood 

 currents and the mixing of fresh and salt water is both 

 rapid and complete. 



The area showed very great differences in salinity, 

 varying from a specific gravity minimum of 1'0048 at 

 the wharf on Thursday, November 27th, on slack tide 

 at 3.30 p.m. to specific gravity maximum of 1*0260 at the 

 same station on Saturday, 1st November, on full flood tide 

 at 10.0 a.m. This particular variation from slightly 

 brackish to heavily salted water is an unusual one, and 

 was largely due to the rainfall distribution immediately 

 precedent to these dates, e.g., the rainfall as registered at 

 Aberdovey itself was 0'77 inches for the week preceding 

 November 1st, and upwards of 1^ inches for the week 

 preceding November 27th, while the differences in the 

 area marking the gathering ground of the Dovey were 

 much in excess of this. 



The general changes in salinities are more or less in 

 accordance with the particular estuarine conditions which 



