■286 Correspondence — R. Ashington Bullen. 



lake and the sea is made of stiff calcareous clay associated with 

 masses of conglomerate resting on plastic clay, that on watery mud, 

 and that again on stiff calcareous clay. The sea-water appears to 

 percolate through the highest deposits, meeting with checks in the 

 conglomerates, and thus reaches the basin somewhat slowly, where 

 it is evaporated to dryness by the summer heat and deposits its salt. 

 Artificial channels have been made, to carry the flood-water from the 

 land direct to the sea, so that it does not dilute the brine of the 

 lake. The rainfall in the catchment-area round the lake is at 

 the most only enough to supply 223 million gallons, and as the lake 

 contains 480 million gallons when full, the balance of 257 million 

 gallons must be derived from the sea. The lake is probably situated 

 on what was an extensive arm of the sea at the close of the 

 Cainozoic ei'a. The salt-harvest begins in August, at the zenith of 

 summer heat, and it is reported that a single heavy shower at that 

 time of year suffices to ruin it. Observations are given on the 

 density of the water, the plants and animals in the water, and the 

 lake-shore deposits. 



Go:RI^:E;sI^OITI^:E]I^^ GE. 



SHELLS FEOM PORTLAND EUBBLE DRIFT. 



Sir, — May I ask a few lines space to add to the list of Land and 

 Fresh-water Shells from Portland Bill Rubble Drift recorded in my 

 previous letter (Geol. Mag., Dec. IV, Vol. I, 1894, p. 431). 



After about three hours' work there on Feb. 21st last among the 

 numerous shells of species already recorded, I found the following 

 new species : Helicella itala, 2 specimens ; Limncea truncatula 

 (dwarfed variety), 4 specimens. These identifications have been 

 kindly endorsed by Mr. Edgar A. Smith, F.Z.S., of the Zoological 

 Department, British Museum (Natural History). 



On carefully going over the specimens with Mr. B. B. Woodward 

 and Mr. A. Santer Kennard, two other species must be recorded, 

 viz.. Helix, sp. (protoconch of an indeterminable species), and 

 Sygromia rufescens (Pennant). The relative abundance of the 

 species, as found by me, is as under, adding previously recorded 

 finds (Geol. Mag., 1894, pp. 431, 432) to those of February 21 last 

 (new records are in italics) : — 

 Helicella itala (Linn.) 

 Hygromia hispida (Linn.) ... 

 Hygromia rufescens (Pennant) 



Vallonia pulchella (Miill.) 



Helix, sp. 



Pupa muscorum (Linn.) 



Succinea oblonga, Drap. 



Limnsea pereger (Linn.) 



Limncea truncatula (Miill.) 



Poraatias reflexus (Linn.) [ = Cyclostoma elegans (Miill.)] 



Pisidium, sp. 



