Mr Grossland, The Coral Reefs of Zanzibar. 493 



The Coral Reefs of Zanzibar. By Cyril Crossland, B.A., 

 Clare College. 



[Read 19 May 1902.] 



Introduction. 



My opportunity for observing the facts upon which this 

 paper is based arose from the enthusiasm for science of Sir 

 Charles Eliot, K.C.M.G., H.M. Consul-General at Zanzibar, and 

 Commissioner for the East African Protectorate, who took me 

 out to assist in his work on Opisthobranch Mollusca. To our 

 disappointment we found the neighbourhood of Zanzibar a poor 

 collecting ground. For nearly a year I made my head-quarters 

 on the east side of the island at Chuaka. At low spring tides 

 Chuaka Bay is a wide expanse of bare sand, and though 

 I found these banks extremely rich in both Polychaeta and 

 Opisthobranchiata, I often wished to be nearer deep water for 

 dredging, and to see the more typical conditions of life on the 

 open coast. At Sir Charles Eliot's suggestion I first visited the 

 Mnemba reef, and that journey made me feel the fascination of 

 boat travel so that afterwards I undertook several other excursions. 

 In this way I gained a knowledge of the reefs from Ras Nnngwe, 

 the northernmost point of the island, to Ras Mkunduchi 1 , which is 

 the south-east corner. 



I wish to express my thanks to the Zanzibar Government for 

 the loan of a boat during my stay. 



Physical Conditions, Seasons. 



The tides rise 15 feet at springs, 10 feet at neaps. On the 

 east coast there is always a northerly current, varying from two 

 to four miles an hour in the south-west monsoon, and from one to 

 three in the north-east. This runs through the channel between 

 Zanzibar and Pemba 'with great velocity' 2 . It is the result of 



1 My authority for place-names is T. J. Last, Esq., Slavery Commissioner of the 

 Zanzibar Government, whose knowledge of the language and of the island exceeds 

 that of any other resident. 



2 The African pilot. 



