158 LEVEL OF LAKE NLCARAGUA 



lake V^asin itself sufficient to produce a decrease in the altitude of its 

 surface amounting to 20 feet would almost certainly have produced 

 more or less tilting of the surface by the subsidence of some portions 

 of the lake's perimeter more than others. It is quite inconceivable 

 that the region should have been wari)ed in such a manner that the 

 lake shore at Las Lajas should be lowered 20 feet, while the Pacific 

 coast, only 12 miles distant, was not affected, and that at the same 

 time every part of the lake shore should also be depressed an exactly 

 equal amount. But if the basin had been unequall}' depressed, some 

 portions of the shore would be drowned, while at other ])oints the 

 lake bottom would be laid bare, and raised beaches left at the former 

 shore line. Nearly the entire circuit of the lake was made by the 

 writer, and its shores were carefully studied with the object of deter- 

 mining whether or not there existed an}' evidence of recent changes 

 in level. Owing to the regularity of the winds which prevail in this 

 region, the different portions of the lake shore present wide differences 

 in character, but there is everywhere a nice adjustment of shore features 

 to present conditions. At the lower end and along the northeastern 

 side, where there is generally an offshore wind and consequently no 

 surf, the streams have built extensive deltas out into the lake, and 

 the surface of the deltaj)lains and floodi)lains is regulated b}-^ tiie 

 fluctuations in height of streams and lake due to seasonal changes. A 

 depression of 6 feet relatively to lake level would permanently flood 

 these deltaplains. while an elevation of equal amount would raise 

 them aiK)ve flood level and start the streams to deepening their chan- 

 nels and building new deltas at lower levels. 



Along the southwestern side of the lake there is a rather heavy 

 surf throughout the greater part of the A'ear. Wave erosion is there- 

 fore progressing more or less rapidl}', according to the character of 

 the rocks. The width of the beach between the water margin and 

 the base of the wave-cut cliff" is everywhere perfectly adjusted to the 

 seasonal fluctuations in level and the character of the materials in 

 which the cliff is cut. Any recent change in the relation of lake 

 level to shore would necessitate a readjustment of these conditions. 

 An elevation relatively to lake level would have raised beaches above 

 the reach of the higiiest flood water. A depression would drown the 

 beach and start the waves to cutting at a higher level. Nothing of 

 this kind was found, and it is certain that the relations of lake level 

 to land have not suffered recent change on this side of the lake. The 

 changes at the upper end of the lake, in the vicinity of Tipitapa 

 River, cited by Professor Heilprin, will be discussed later. 



