11 
side of each claire is cut down to the depth at which it is'wished to keep the water; this depression com¬ 
municates with the nearest gully or natural channel, and at spring tides (when only the water in the tides 
can be changed) the tide, winding its way up the channel, finds ingress and egress. The same channel also 
serves to carry away the ■waste water whenever it is Avished to lay the pits dry, for which purpose the 
simple method is adopted of digging a hole in the clay bank, whicli is readily stopped up again when 
desired. 
During the summer months the sea has free ingress and egress to the claires to purify them, and 
the coating of blackish mud Avliich has collected on tlio surface during the preceding year is also removed. 
In August they usually stop up the gaps in the banks, in order that the continued action on the soil and 
water may produce the greenish creamy scum with which tlie surface mud of all the claires is covered. 
Oysters in the claires do not begin to fatten until late in the autumn and winter. A large quantity of 
oysters will live well in the pits, but they will not fatten if too numerous. There is no doubt that the 
fewer oysters that arc placed in a pit, tlio more food there will he for each of them and the quicker they 
will fatten. WliercA'cr these claires have been constructed they have succeeded, and, when once constructed, 
the labour and expenso of working them are small. The claires at Marennes occupy a strip of low-lying clay 
country on the river Seuclre. The soil is marl, that is, a mixture of chalk and clay, aiul is of various colours— 
greyish, blue or black, greyish yellow, and in some eases red. The muddy or marly bottoms are most favour¬ 
able to the growth and fattening of the oyster. Professor Sullivan says, “ the soil of all places successful 
as oyster fattening stations contains more or less of a fine fiocculent highly hydrated silty clay, abounding 
in vegetable and animal matter, derived chiefly from diatomacca, rhizopoda, and other microscopical organ¬ 
isms ; and that the soils of those places which lui've proved successful as breeding stations always contains 
some of it, but not necessarily as much as those which fatten ; and lastly, that in those places which have 
proved failures, this peculiar kind of mud is either, wholly absent, or inferior in quality and quantity.” 
13. The Royal Commission (Irehvnd) say, fruitful oyster mud may vary within very "wide limits, from 
almost pure sand to almost plastic clay. In the very sandy grounds, there must, however, be always a 
sufiicient quantity of highly hydrated clay to render the sand adhesive and to preserve it from becoming a 
mere loose running mass. 
14. In the clayey grounds tliere must always be calcareous mud to make the clay porous and prevent 
it becoming too hard,—clay marls, with some intermixed sand, being perhaps the best of all materials for 
oyster grounds. 
15. The earth known as the London clay appears to be the soil peculiarly adapted for oysters. It may 
be well here to explain that the term “ London clay” is employed in a general and a special sense. In the 
former it is used as a collective name for a number of beds of the old tertiary formation, consisting of 
gravels and sands below and of clays above. In the special or limited sense, it is applied to the bluish 
or blackish clay, sometimes mixed with a greenish coloured earth and Avhito sand, which forms the upper 
parts of the beds just mentioned. London clay is plastic clay, not differing much in chemical compositioK 
from ordinary potters’ clay. All fruitful oyster muds contain organic matter, always duo, in part, to the 
presence of infusoria, and sometimes, in part, to small algaj or eonferova?, remains of shell fish, and 
other marine creatures. 
IG. Bertram says, one of the most lucrative branches of oyster farming in France is the fattening of 
oysters in claires, at Marennes,-which have been brought from the lie de Re breeding pares. lutheclairen 
the oysters become green, and of considerably more value than the white oyster. The peculiar colour 
and taste of the green oyster are imparted to it by the vegetable substances which grow in the 
claires. The industry carried on at Marennes consists chiefly of the fattening in claires; and 
the oysters operated upon were at one period of their lives as white as those which are grown at 
any other place ; indeed, it is only after they have been steeped a year or rivo in the muddy ponds 
(claires) of the river Sendre that they attain their much-prized green hue. Ihe ponds (claires) for 
the manufacture of these green oysters—the oyster par excelloice, according to all epicurean autliority 
require to he watertight, for they are not submerged by the sea, except during very high tides. Each 
claire is about 100 ft. square; the walls for retaining the w'aters require, therefore, to he very strong. 
They are composed of low banks of earth, iivc or six feet thick at the base, and about 3 ft. in height. These 
walls are also useful in forming a promenade, on which the watchers or workers can walk to and fro and 
view the different ponds. The floodgates for the admission of the tide require also to he thoroughly 
watertight and to fit with great precision, as the stock of oysters must always be covered with water, hut 
a too frequent flow of the tide over the ])onds is not desirable, hence the walls, which serve the double 
purpose of both keeping in and keeping out the water. A trench or ditch is cut in the inside of each 
pond, for the better collection of the green slime left at each flow of the tide ; and many tidal inundations 
are 
