266 MacCauGHEeEy: THE STRAND FLORA 
of an island like Hawaii steadily decreases until ultimately the 
condition exhibited by the tiny strand of Laysan or Midway is 
reached. In this manner the subsidence-factor, although not of 
especial force at any one time, has been through long periods of 
time a powerful influence on the strand flora. 
Although subsidence has been the dominant note in Hawaii’s 
geological history, there have been minor elevations within recent 
times. Raised coral reefs and beaches occur at various points 
along the coasts, e. g., along the southern and western shores of 
Oahu. The highest reef known is on the southwestern end of 
Mailiilii, elevated 120 feet above the sea. Just as local elevation 
at such points as Mokapu, Kalihi, and the Coral Plain has pushed 
the littoral zone seaward, so at Hanalei, Kahana, Kaneohe, and 
Pearl Harbor the drowning or submergence of valley-mouths has 
developed deep embayments, and the littoral flora extends deep 
into the lowland zone which surrounds it on three sides. It is 
evident that sufficient study and emphasis has not been given to 
the ecological effects of these gradual changes of land- and sea- 
level. 
In his illuminating studies of the New Zealand flora, Aston 
(’12) concludes that the raised marine beaches at Cape Turakirae 
show that there has occurred comparatively recently, and perhaps 
within historic times, rapid elevation of the coast line. Violent 
earthquakes have so altered the physiography of the littoral as to 
result in some unusual ecological features. 
ORIGIN ' 
RELATION OF PACIFIC OCEAN CURRENTS TO THE DISSEMINATION 
OF PLANTS OF THE HAWAIIAN LITTORAL 
The importance of ocean currents as agencies for the distri- 
bution of plants, and more particularly for the wide dissemination 
of beach species, has long been recognized. In a vast body of 
water, like the Pacific, dotted with thousands of scattered islands, 
the surface currents assume special significance in relation to the 
migrations of plants, animals, and man. 
The surface circulation of the Pacific is, on the whole, notably 
less active than that of the Atlantic. The vertices of the rota- 
tional movements are marked by “Sargasso Seas”’ in the north and 
