236 PHYSIOGRAPHY OF NICARAGUA CANAL ROUTE 



Summing up the foregoing state- 

 ments very briefly, it appears 

 that the surface of the Nicaraguan 

 depression consists of a broadly 

 undulating plain formed by the 

 erosion of streams flowing to the 

 Pacific and to the Atlantic from 

 low gaps at the divide. Above 

 this plain are residual hills, most 

 abundant at the axis of the isth- 

 mus, where the continental divide 

 was formerly located, but increas- 

 ing in height along the axis to- 

 ward the north, where they merge 

 with the mountains of northern 

 Nicaragua, and final]}', there are 

 many valleys which have been 

 cut in the surface of the plain by 

 the erosion of streams after the 

 region had been elevated to a 

 higher altitude. The lower por- 

 tions of these valleys have subse- 

 quently been drowned and silted 

 up with the formation of broad 

 alluvial flood plains. 



During most of the time in 

 which these topographic features 

 were being developed the Pacific 

 coast had an outline very different 

 from that which it has at present. 

 Lakes Nicaragua and Managua 

 then had no existence, and the re- 

 gion which they now occupy was 

 in part the basins of streams flow- 

 ing to the Pacific, in part open 

 ocean, and in part a bay which 

 then indented the Pacific coast 

 and whose southern point was 

 near the present island of Madera. 

 The relations of the present and 

 former coast lines are shown on 

 the accompanying map, plate 6. 



