36 THE NATURALIST IX NICARAGUA. [Hi. III. 



survey is made across from sea to sea, there can be no 

 doubt tbat at this point occurs the lowest pass between 

 the Atlantic and the Pacific in Central America. This 

 fact, and the immense natural reservoir of water near the 

 head of the navigation, point out this route as a practi- 

 cable one for a ship canal between the two oceans. 



Instead of cutting a canal from the head of the delta 

 of the San Juan to the sea, as has been proposed, the 

 Colorado branch might be straightened, and dredged to 

 the required depth. Higher up, the Torre Castillo and 

 Machuca Rapids form natural dams across the river. 

 These might be raised, locks formed round them, and the 

 water deepened by dredging between them. In this way 

 the great expense of cutting a canal, raid the fearful 

 mortality that always arises amongst the labourers when 

 excavations are made in the virgin soil of the tropics, 

 especially in marshy lands, would be greatly lessened be- 

 tween the lake and the Atlantic. Another great ad- 

 vantage would be that the deepening of the river would 

 be effected by steam power, so that it would not be re- 

 quired to bring such a multitude of labourers to the 

 isthmus as would be necessary if a canal were cut from 

 the river ; the whole track, morever, passes through 

 virgin forests rich in inexhaustible supplies of fuel. 



San Carlos is a small town at the foot of the great 

 lake, where it empties its waters into the San Juan 

 river, its only outlet to the ocean. On a hill behind the 

 town, and commanding the entrance to the river, are the 

 ruins of a once strong fort built by the Spaniards, the 

 crumbling walls now green with the delicate fronds of a 

 maidenhair fern (Adiantum). The little town consists of 

 a single rugged street leading up from the lake. The 



