52 USEFUL PLANTS OF GUAM. 
is easily worked. In certain localities nodules of flint are found simi- 
lar to those from European chalk formations. 
Rrvers.—In the northern portion of the island the ground is so 
porous that the water disappears as it falls. There are, however, a 
number of sink holes called lupog, and in the rainy season several 
small streams near the bases of the hills of Santa Rosa and Matdguag. 
Near the middle of the island about a mile anda half from Agafia 
there is a fine large spring or lake (Matan-hanom) from which a 
copious supply of water issues all the year round. This, after 
slowly oozing through the great swamp called the ‘* Ciénaga,” forms 
the Agafia River, the channel of which has been artificially length- 
ened and turned for about a mile parallel to the coast before it 
reaches the sea. This is for the purpose of affording a laundry to the 
women of Agafia. In the southern portion of the island there are a 
number of small streams on both sides, some of which lose themselves 
beneath the surface for a time and reappear, issuing from caverns. 
VEGETATION OF THE ISLAND. 
PLANT COVERING ACCORDING TO HABITAT. 
CORAL REEFS. 
Among the alge growing on the reef the most conspicuous are the 
brown Padinas with fan-like fronds expanded like the tail of a strut- 
ting peacock, jointed Halimedas, like miniature Opuntias, and the 
eathery Caulerpa plumaris. Another Caulerpa (C. clavifera woi- 
ie ra), green and succulent, looks as though it bore bunches of minia- 
ture grapes. Among the red alge are the more delicate Acanthophora 
orientalis, Corallopsis salicornia, with terete cartilaginous fronds, and 
Mastophora lamourouxi’, with dense foliaceous fronds, somewhat like 
Chondrus in form, and conspicuous fruit. From some of the gelati- 
nous species the natives make blanemange. Among the more delicate 
green forms are the woolly Rhizoclonium tortuosum and the beau- 
tiful little Bryopsis plumosa. Near the mouths of rivers grow 
Enteromorpha clathrata and E. compressa, with narrow, linear, grass- 
like fronds. (See Alge, catalogue.) Among the marine flowering 
plants are //alodule uninervis, a plant resembling a fine eelgrass (Zos- 
tera), and /alophila ovata, belonging to the Vallisneriaceae, with a 
creeping rootstock and oval or linear-oblong petioled leaves. 
MANGROVE SWAMPS. 
At the mouths of many streams, where the water is brackish and 
the shores are muddy, are growths of mangrov es and their allies, 
a The principal - cavern of this nature is that in the valley of the TalofOfd River, 
about a mile from its mouth, 
