EIVERS AND LAKES OF NICAEAGUA. 279 



unnavigable by vessels drawing move than ûve or six feet of water. It stands at 

 a mean altitude of 140 feet above the sea. 



Nicaragua, the Cocibolco of the natives, stands some 30 feet lower, or about 110 

 feet above sea-level. It has a mean area of 3,600 square miles ; but there are no 

 abysses as in the Alpine lakes, the deepest cavity being scarcely 280 feet deep. 

 Some parts, especialh' near the San Juan outlet, are very shallow, and the general 

 level varies with the seasons little more than seven or eight feet. But there can 

 be no doubt that it formerly stood at a much higher level, for the islets south of 

 Zapatera are covered with scoriae containing freshwater shells, like those still 

 found on the neighbouring shores. 



During the rains vast spaces round the lake are transformed to absolutely 

 impassable cienagas (quagmires), the waters from the surrounding heights pene- 

 trating to a great depth into the pasty soil and converting the plains into a sea of 

 mud. In the dry season the moisture evaporates, and the baked ground becomes 

 fissured without anywhere clothing itself with vegetation. 



Nicaragua is fed by numerous affluents, some of which have acquired a certain 

 celebrity in connection with various schemes of interoceanic canalisation ; such 

 are the Rios Sapoa and de las Lajasin the isthmus of Rivas. But the most copious 

 tributary is the Rio Frio descending from the Costa Rica uplands, and washing 

 down vast quantities of volcanic sediment, which is gradually filling up the 

 southern part of the basin, and raising its bed above the surface, as the neighbour- 

 ing Solentiname archipelago has already been raised. Then the Rio Frio will 

 become a tributary, not of the lake, but of the San Juan, and this river, thus 

 charged with sedimentary matter, will form a chief obstacle to the proposed 

 interoceanic canal^ 



The San Juan, which escapes from the lake just below the mouth of the Frio, 

 flows in a very sluggish stream till it approaches the Castillo, a little fort on the 

 right bank 40 miles below the outlet. Here the river has forced a passage through 

 the schistose ridge connecting the Chontal mountains with the Costa Rican Cerros 

 de San Carlos. The rapids thus formed are followed some 12 miles lower down by 

 another series of erosions, the vandal de Machuca, so named from the first Euro- 

 pean explorer of the San Juan. Farther on the mainstream is joined by the San 

 Carlos, which sends down from the Costa Rican uplands a volume almost equal to 

 that of the San Juan itself. A little above the delta follows the still more copious 

 Sarapiqui affluent, which also descends from the Costa Rican mountains, but which 

 is so charged with alluvial matter that the idea of utilising the lower course of 

 the San Juan for the proposed canal has been abandoned. 



In the delta itself the shifting branches of the mainstream are joined by 

 the Rio Colorado, a third affluent from Costa Rica. About the middle of the 

 century nearly all the united waters of the San Juan basin entered the sea at 

 Gray town (San Juan del Norte), where the powerful current had excavated a 

 spacious harbour accessible to vessels of average draught. But most of this 

 current was deflected by the opening of the Jimenez, a branch of the San Juan, 

 which now joins the Colorado and which usually bears the same name. Other 



