LEVEL OF LAKE NICARAGUA . 157 



portion of the isthmus without warping ; (2) a depression of the lake 

 basin by warping, the sea margins remaining constant; (3) a cutting 

 down of the lake outlet. 



(1) If the whole isthmian region had undergone recent subsidence, 

 the evidence of such a change would be manifest at the coast. Grey- 

 town is located upon a low sandy beach, which was thrown up by 

 the surf, and has within the past centur}'- been cut off from the sea by 

 a sand spit which inclosed first a harbor and then a closed lagoon. 

 This land has not been added to since it was exposed to the surf early 

 in the century, and any change in elevation, even of a few feet, would 

 be quickly apparent and would be a matter of record. The surface 

 of the San Juan deltaplain ascends from the margin of the sea with 

 a regular gradient merging at its inner margin with the floodplain, 

 as determined b}^ the volume and load of the river. This regular 

 gradient precludes the possibility of any recent change in altitude of 

 this region. Even a slight subsidence would permanently flood ex- 

 tensive areas, and a corresponding rise would cause the streams to 

 deepen their channels so that the flood waters Avould no longer over- 

 top the banks. 



The same evidence of stability is in general true of the Pacific coast. 

 The streams flowing to the Pacific from the divide opposite the south- 

 ern erjd of the lake occupy, in their lower courses, drowned channels 

 which have been more or less completely silted up. Any recent de- 

 pression of the coast would have flooded these alluvial valleys and pro- 

 duced irregularities in their gradient. No such flooding is observed, 

 but, on the contrary, unmistakable evidence that present conditions 

 have prevailed for a considerable time, certainly for several centuries. 

 In the vicinity of Corinto, on the Pacific coast, northwest of the de- 

 pression which holds lakes Nicaragua and Managua, there has been 

 a recent subsidence of a few inches, and this is well recognized by the 

 l)eople of the region, and its amount has been determined by the engi- 

 neers of the railroad which runs from Corinto to Momotombo. This 

 shows that rapid changes of level even of small amount are quickly 

 recognized, and that a depression of 20 feet of any occupied portion 

 of the coast could not i)Ossibly escape notice. 



(2) Lake Nicaragua is about 100 miles long and 45 broad. It for- 

 merly extended eastward at least 25 miles fartiier to the present posi- 

 tion of Castillo Hapids. Now it has been shown above that the coast 

 on either side of the isthmus, at least opposite the southern end of 

 the lake, has not suffered recent subsidence. A depression of the 



