36 Mr Grossland, The Coral Reefs of Pemba Island 



The Coral Reefs of Pemba Island and of the East African 

 Mainland. By Cyril Crossland, B.A., Clare College. 



[Read 10 November 1902.] 



The following observations form a continuation of my paper 

 on the Coral Reefs of Zanzibar 1 . It is only necessary, therefore, 

 to draw comparisons between these reefs and those of Zanzibar. 



Pemba Island 2 . 



Physical conditions. 



The tides rise 12 ft. at spring, 8 ft. at neap, being thus consider- 

 ably less than those of Zanzibar. The northerly current is slightly 

 less strong, varying from one to three knots in the S.W. monsoon 

 up to two knots in the N.E. Tidal currents are of course very 

 strong in the long bays of the west coast. 



The seasons are the same as in Zanzibar, but the rainfall is 

 much heavier. This fact and the abundance of soil has made 

 Pemba the Emerald Isle of the Arabs, to whom it is known as 

 El Huthera, The Green. 



Structure of the Island. 



Pemba lies between latitudes 4° 50' S. and 5° 30' S., the line of 

 longitude 39° 45' E. almost bisecting it longitudinally. It is thus 

 about 40 miles long with an extreme breadth between the reefs of 

 the west coast and those of the east of sixteen miles. 



The results of wave and current erosion on the original mass 

 of rock and sand are much the same as in the case of Zanzibar, 

 viz. a regular and comparatively slight erosion of the more 

 uniformly hard rock of the east coast and a deeper and very 

 irregular irruption into the west, which is formed of materials of 

 varying hardness. 



The materials of the island are the same as those of Zanzibar, 



1 Camb. Phil. Proc. xi. 493. 



2 For my opportunity of visiting Pemba I am indebted to the Zanzibar Govern- 

 ment, especially to Mr Bomangi, Minister of Public Works, whom I accompanied on 

 a visit to the lighthouse in course of erection on Ras Kegomache, the northernmost 

 point of the Island. I owe my exploration of Chaki Chaki Bay, Mesale Islet, and 

 the East coast to the hospitality of the Missionaries of the Society of Friends of 

 Banani. 



