A Botanical Expedition to Nicaragua. 365 



is probable that at one time the lake extended over this por- 

 tion of the river- valley, and that its waters were at least 12 

 or 15 feet higher than at present before the river had cut 

 down to its present bed through the barrier near o^- below the 

 mouth of the Los Sabalos River. 



Below the Los Sabalos the San Juan River is much more 

 rapid, and a number of rapids, of which those at Castillo are 

 the most formidable, offer a serious impediment to navigation 

 during the dry season. From the Los Sabalos River to Cas- 

 tillo the river valley is quite narrow, the low rounded hills 

 approaching close to the river. Below Castillo to the Ma- 

 chuca Rapids, a distance of about 15 miles, the river valley is 

 somewhat broader, the hills being mostly rather low and only 

 in some places approaching the river. For a short distance 

 below Machuca on the Costa Rica side the hills are close to 

 the river, and higher, some of them probably reaching 500 

 feet in height. Beyond this and continuing about 25 miles 

 to Ochoa, the proposed site of the great dam b}- which the 

 waters of the San Juan are to be brought to a level with the 

 lake, the course of the river lies between low hills which alter- 

 nately approach the river on either side, those on the Costa 

 Rica side beincf rather higfher and more numerous. Below 

 Ochoa the river is wider and contains more islands, and its 

 valley becomes broader and flatter and in many places is 

 swampy, particularly below Colorado Junction, the point at 

 which the greater part of the water in the river leaves the 

 San Juan river-bed and forms the Colorado branch. This 

 point is over 30 miles below Ochoa, and about 20 miles above 

 the mouth of the Colorado. Both the old San Juan branch 

 and the Colorado branch flow through low swamps which 

 extend from Colorado Junction to the sea, and which are uni- 

 formly covered with an inextricable tangle of tropical vegeta- 

 tion. 



The San Juan valley, with the adjacent country, forms a 

 great depression which cuts the Cordillera, "the back-bone of 

 the continent," and widely separates the segments, the moun- 



