xxii INTRODUCTION. 



mies compared to the gigantic masses moved on some of the reef flats of the 

 Pacific Islands. The boulder belts of the Maldives seem like a newly 

 macadamized road as compared to the quarry blocks which often line miles 

 of the beaches of some Pacific atolls. But the same forces are at work in 

 the Maldives only on a diminutive scale, even during the prevalence of the 

 southwest monsoon. The beaches both sand and shingle are as a whole 

 remarkably steep ; they rarely rise to more than five or six feet, though in 

 some of the northern atolls they are fully twelve feet high. Mr. Gardiner 

 informs me he has seen dunes rising to twenty-eight or thirty feet in height. 



The Maldives are remarkable for the small amount of coral breccia and 

 cono'lomerate or beach rock which is rehandled. The material moved upon 

 the reef flats is nearly all coral sand, — a great contrast to the Pacific atolls, 

 where the wearing and crushing and rehandling of the reef rock ledges, both 

 old and recent, are the most prominent features in the modification of the 

 reef flats of the Gilbert, Ellice, Marshall, and Paumotu Islands. 



There exist in the Maldives, it is true, a number of shingle beaches and 

 boulder beaches on some of the islands exposed to the full action of the 

 southwest monsoon both in the southern and northern part of the group ; 

 but these beaches are insignificant as compared with the wide reef flats and 

 beaches of the Pacific atolls, which are strewn for miles with shingle and 

 boulders often of a great size. This marked difference is due in the one 

 case to the comparatively feeble sea and rollers of the southwest monsoon, 

 in the other to the huge rollers of the southeast and northeast trades acting 

 continuously with a force which bears no comparison to the forces at work 

 in the Indian Ocean. 



Mr. J. Stanley Gardiner spent over three months at Minikoi ; he has 

 given a detailed account of the atoll.^ According to him the sea is rapidly 

 encroaching upon the east face of the island. He looks upon the Minikoi 

 conglomerate, found at the base of the outer beach, as a reef rock similar to 

 the conglomerate I have observed at so many of the Pacific atolls ^ ; show- 

 ing that Minikoi, as well as the Pacific atolls, must at one time have been 

 subject to a slight elevation (which he places at twenty-four feet). The 



1 Loc. cil., p. 13. 



2 A. Agassiz, Mem. M. C. Z., Vol. XXVIII., Pis. 8, 11, 12, 40, 63, 135, 136, 158, 163, 171. 



