48 REPORT ON OYSTER CULTURE 



(1.) The temperature of the sea on the coast of Ireland varies 

 within narrower limits than on the coast of Great Britain and 

 France, or, in other words, it is more equable throughout the 

 year, and also throughout the season of oyster breeding. 



(2.) During the summer months, especially on the south and 

 west coasts of Ireland, the temperature at noon, and, therefore, a 

 fortiori between two and three in the afternoon, is generally suf- 

 ficiently high to fulfil the conditions as regards temperature re- 

 quired for the abundant production of healthy oyster spat. This 

 conclusion is especially true for the months of July and August, 

 and with high water about two or three hours afternoon. 



(3.) The winter temperature of the sea on the Irish coast is 

 such as to render the destruction of oyster beds from excessive 

 cold a contingency that may be considered as never likely to occur. 



(4.) The second of these conclusions applies equally to the 

 greater part of the coast of Great Britain, and the third to its south 

 and west coasts. 



A reference to the Abstract of the Tables of Temperature shows 

 that latitude most powerfully influences the temperature of the 

 sea ; next, the situation of the place according as it is on an 

 eastern or western shore (this probably being the effect of the 

 Gulf Stream) ; lastly, there are local conditions, such as the shelter 

 afforded by surrounding mountains, deep bays, inlets, &c., which 

 during the summer months tend to give to the waters of such 

 places an exceptional degree of heat. 



The general inference being that western coasts are less liable 

 than the eastern to great variations, although there are but few 

 places even on the eastern coasts where this variation is so great 

 as to prevent oyster culture being successfully adopted. 



However, it is to be noticed that there prevails throughout the 

 whole series of tables a higher degree of warmth close to the 

 shore in summer than at some distance at sea. This might be 

 naturally expected from the greater influence of the sun upon the 

 soil over which there is a relatively less depth of water in accord- 

 ance with the remarks made by Professor Hennessy at the end of 

 his report, p. 75. 



By our desire Professor Hennessy also laid down on the map 

 which accompanies this report (see plate 10, Appendix) various 

 lines showing the distribution of temperature over Ireland and on 

 the surface of the surrounding sea. We have also indicated on 

 the same map the site of all the natural oyster banks as far as we 

 were able to ascertain them. For this purpose the queries in 

 Appendix I. were sent to the various coast-guard stations. 



The analysis of the earths was intrusted to Professor Sullivan. 

 His report will be found in the Appendix H. 



We have arrived at the following conclusions from the im- 

 portant information afforded by it : — 



1. As regards mineralogical constitution, the mud of oyster 

 grounds, suitable both for reproduction and fattening, may be de- 

 rived from almost any kind of rock. 



2. As regards mechanical character, fruitful oyster mud may 

 vary within very wide limits from almost pure sand to plastic clay. 

 In the very sandy grounds there must, however, be always a suf- 



