334 C. W. HAYES — GEOLOGY OF NICARAGUA CANAL ROUTE 



with a suspension of the volcanic activity. The extent of the land 

 after the uplift can only be determined in a very general way. It is 

 probable that the Pacific coast was some distance farther southwest than 

 at present, and there ma}^ have Ijeen volcanic peaks along this coast 

 which have subsequently been entirely removed by marine erosion. 

 The isthmus was very likely somewhat broader than now, although the 

 elevation was such that Siuy particular rock stratum was from 100 to 

 200 feet lower than at the present time. The uplift inaugurated a period 

 of active degradation. It is probable that the surface at the beginning 

 of this period was in general broadly undulating, with perhaps isolated 

 volcanic peaks, but no distinct mountain chain. The uplift was accom- 

 panied by only moderate warping and tilting of the surface, for the Ter- 

 tiary beds have suffered comparatively little disturbance up to the present 

 time. Their average dips are between 10 and 15 degrees. In general 

 the character of the deformation was such as to produce a series of gentle 

 folds, whose axes are approximately parallel with the coastlines. This 

 was doubtless accompanied by more or less faulting, although evidence 

 of the latter is very meager. 



The character of the present drainage makes it evident that no struc- 

 tures wei'e developed in the region sufficiently well defined and pro- 

 nounced to have a marked influence on the direction of the drainage. 

 The stream courses, with the exceptions which have been already noted 

 and which will be explained later, are such as would have resulted from 

 normal stream development on a low, gently undulating arch. 



The region now occupied by the Nicaraguan depression appears to 

 have been originally the lowest and narrowest portion of the isthmus ; 

 hence its surface was more nearly reduced to baselevel during this degra- 

 dation period than that of the broader portion to the north. A some- 

 what perfect peneplain was developed along its margins, and broad base- 

 leveled valleys were extended well back to the divide, in which there 

 were numerous low broad gaps. Although the position of the coastlines 

 at the beginning of this period is not easily determined, their position at 

 its conclusion may be made out with a fair degree of probability. The 

 Atlantic coast was perhaps about where it now is, or possibly a little 

 farther east than at the present time, for although it has subsequently 

 been moved westward by submergence and by marine erosion, it has 

 also been considerably extended b}'' emergence and by deposition, so 

 that its oscillations have about balanced each other. The Pacific coast, 

 on the other hand, differed materiall}'- in outline from the present. As 

 already indicated, lakes Nicaragua and Managua then had no existence, 

 and the coastline occupied a position somewhat near that represented on 

 the accompanying outline map, plate 30, although the line there shown 



