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theuiselves and may, on thaï ground, be considered as true, 

 though small. •• Lakes. •■ 



THE TIDES AND THE CHEMICAL CONDITIONS 



Sucb being the pasfc liistory and présent conditions of the 

 Broads District, f it is part of ourobjecl lo study the physical 

 conditions of this distrid regarded asasystèm oftidal waters. 

 We hâve to know how Far the present| l'auna is affected by the 



past conditions and by the présent tides. We hâve, therefore, 

 carriedoul preliminary investigations by means of chemical ana- 

 hsis and by the use of portable tide gauges. As the resuit of 

 the work donc by the staff of tlie Laboratory and by Messrs. 

 [nnes and Peel, il seeins sullicicni ly clear that, in ordinary 

 conditions, the salinity of tlie River Bureis not affected by the 

 tide i'urtlier than Acle Bridge (12 miles from Yarmouth). 

 Our observations show tlial the salinity at any point is subjeçt 

 to gréa t and perplexing variations, but thai thèse variations are 

 not approximately referable to tidal periodicity in tlie river above 

 Acle even during ordinary spring tides. 



On the other ïiand there are, at times, tides of abnormal 

 heigth, due, as a rule, to prolonged North-Wesi winds. At 

 thèse limes a body of sali water is driven up tlie river to agréai 

 distance carrying with il a purely marine l'auna, including such 

 forms as Cténophores and marine Calanoids. In thèse eir- 

 cumstances there may be an appréciable rise of salinity as far 

 from tlie sea as Sut ton Broad(2o miles from Y a rmoul h), and 

 doubtless also as far up the Bure as Wroxhain. Probably the 

 salinity is affected toagreater distance than the sait water itself 

 pénétrâtes, tlie sait passingon by diffusion. Thesteady increase 

 of salinity vvhich may beobserved in tlie river from AntMouth 

 downwards is no doubl due to diffusion, since there is normally 

 no tidal variation in salinity above Acle. Tlie restoration of 

 normal conditions after an exceptional tide may take several 

 weeks. 



In tlie Thurne river the conditions are reversed. Analyses 

 taken at différent points from Thurne Moutli upwards show a 

 progressive increase in salinity, culminating in Horsey Mère, 

 where there may be as much as 66 grains of Chlorine per gallon. 

 There can be no doubl that this liiu.li salinity is due lo the 

 existence of sait springs in Horsey Mère and probably also, 



