OF THE HAWAIIAN ARCHIPELAGO 497 
disintegrates into mud. The main part of the tufa platform is 
wave-swept and barren of vegetation; the upper portion is the 
habitat of such forms as Nama sandwicense, Sicyos hispidus, Jac- 
quemontia sandwicensis; Tribulus cistoides, Cenchrus calyculatus, 
Waltheria americana. te 
Tufaceous sand or mud is brownish or yellowish green in color, 
much finer in texture than the coral sand, and much more retentive 
of moisture. It often contains large quantities of olivine; this 
imparts the greenish hue. Some common plants of the muddy 
beaches are: Batis maritima, Polypogon littoralis, Thespesia 
populnea, Ruppia maritima, Cyperus laevigatus, Chenopodium 
album. 
A number of small islets, such as Moku Manu, Manana and 
Molokini, are made up largely or wholly of tufaceous deposits, and 
represent the eroded remains of former tufa cones. 
6. Coral limestone strands.—Within recent geological times 
there has been a slight uplift at various points in the Archipelago, 
which has resulted in elevating above sea-level broad shelves of 
coral limestone. Such areas are especially abundant on the island 
of Oahu, and portions of the shore around Pearl Harbor, Kaneohe 
Bay, Waianae, Kahuku, and Barber’s Point are formed of the 
exposed coral limestone. These shores are often undercut by the 
surf, and are sculptured from above by the action of rain-water. 
The limestone along the beach may be actually wave-washed, or 
may be more or less buried beneath coral sand. Further back 
from the shore it is usually covered with a layer of soil. 
7. Coral sand.—Beaches of pure coral sand are abundant on 
the islands of Oahu and Kauai, and also occur on the islands of 
Maui and Molokai. On the coral atolls to the leeward the coral 
strand is, of course, dominant. The sand is washed ashore from 
the coral reefs, and sometimes accumulates in sufficient quantities 
to form dunes. Mana, Kauai, Makaha and Heleloa, Oahu, and 
West Molokai, are representative dune regions. Fine stretches of 
coral beach may be found at Waikiki, Makapuu, Waimanalo, 
Mokapu, Kanuku, Waianae, and Ewa. 
The Hawaiian coral strands correspond to the xerophytic 
beaches of Cowles (’99, p- 112), who recognizes two classes of 
beaches: hydrophytic and xerophytic, defining the latter as essen- 
