1 CO LE I 'EL OF LA KE XK'ARA G UA 



the materials are being transported northward, it is easy to under- 

 stand how rapid changes might take place in the character of the 

 Tipitapa River and convert it in a few years from a deep estuary to a 

 shallow lagoon. The amount of water passing through the Tipitapa 

 River is entirely independent of the elevation of Lake Nicaragua, 

 since it depends wholly upon the relation between rainfall and evap- 

 oration in the basin of Lake Managua. Changed conditions at the 

 head of the lake therefore do not in any way support the contention 

 that the level of the lake has fallen in recent times. 



It might be inferred from Professor Heilprin's article that Lake 

 Nicaragua is in the heart of a volcanic region subjected to frequent 

 destructive earthquakes. This subject of volcanism and the proba- 

 bility of earthquakes of sufficient intensit}' to injure canal structures 

 is fully discussed in the recent report of the Canal Commission. It 

 need only be stated here that the canal region lies midway between 

 the Costa Rican volcanoes to the south and the Nicaraguan volcanoes 

 to the north, and that the volcanic activity in V)oth these groups is 

 evidently on the wane. No earthquake of destructive violence has 

 visited the canal region since its occupanc}^ by the Spaniards, and the 

 two centers of the moderate seismic activity, namely, Irazu on the 

 south and the Maribios Range on the north, are respectively 60 and 

 100 miles from the nearest portions of the canal route. 



The quotation from the English engineer Colquhoun indicates that 

 the latter was a superficial observer whose conclusions were drawn 

 from a relatively short period of observation. It is quite true that 

 the amount of water flowing in the lower San .Juan is becoming 

 smaller each 3'ear, but this is due to a corresponding increase in the 

 Rio Colorado, which is now the main distributary from the head of 

 the delta to the sea. This successive transfer of the main channel to 

 more southerl}^ distributaries has been fully discussed in the report 

 above cited. Even between the head of the delta and the mouth of 

 the San Carlos one is impressed in the dry season with the insignifi- 

 cant volume of the Rio San Juan, and if one's observations were con- 

 fined to tliis period he might readil}'^ believe that a permanent dimi- 

 nution in the volume of the stream had taken i)lace. This, however, 

 is merely a seasonal fluctuation. 



Professor Heilprin's citation of the fluctuation in altitude of various 

 lakes, as Great Salt Lake and Lake Tanganyika, has no bearing what- 

 ever upon the question, since these are inclosed lakes and the observed 

 great fluctuation of their levels is directl}^ connected with C3'cles of 



