52 USEFUL PLANTS OF GUAM. 



is easily worked. In certain localities nodules of flint are found simi- 

 lar to those from European chalk formations. 



RIVERS. 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 Mataguag. 

 Near the middle of the island about a mile and a half from Agana 

 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 " Cienaga," forms 

 the Agana 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 Agana. 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. a 



VEGETATION OF THE ISLAND. 

 PLANT COVERING ACCORDING TO HABITAT. 



CORAL REEFS. 



Among the algae 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 

 feathery Caulerpa plwnaris. Another Caulerpa (C. davifera uvi- 

 fera), green and succulent, looks as though it bore bunches of minia- 

 ture grapes. Among the red algae are the more delicate Acanthophora 

 orientalis, Corallopsis salicornia, with terete cartilaginous fronds, and 

 Mastopliorcb lamourouxii, with dense foliaceous fronds, somewhat like 

 Chondrus in form, and conspicuous fruit. From some of the gelati- 

 nous species the natives make blancmange. Among the more delicate 

 green forms are the woolly Rhizodonium tortuosum and the beau- 

 tiful little Bryopsis plumosa. Near the mouths of rivers grow 

 Enterorrwrpha dathrata and E. compressa, with narrow, linear, grass- 

 like fronds. (See Algae, catalogue.) Among the marine flowering 

 plants are Ilolodule uninervis, a plant resembling a fine eelgrass (Zos- 

 tera), and Ilolophila 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 mangroves and their allies, 



The principal cavern of this nature is that in the valley of the Talofofo River, 

 about a mile from its mouth. 



