CHARACTER OF GEOLOGICAL OBSERVATIONS 287 



was obtained concerning the geology immediately upon the canal route, 

 but little opportunity'' was afforded for a general examination of the 

 adjacent region. The conditions which prevail over much of the coun- 

 try, however, especially the presence of a luxuriant tropical vegetation 

 and the depth of rock decay, entirely prevent, or at least greatly hamper, 

 ordinary geological field-work. The only way in which reliable infor- 

 mation concerning the underlying rocks can be obtained is therefore by 

 means of the drill. The lack of more extended observations is most 

 seriously felt in the paucity of information concerning the physiography 

 of the region on either side of the San Juan river formerly occupied by 

 the Continental divide. This region is densely forested, and, having no 

 roads, is very difficult of access. It contains very few permanent habi- 

 tations, and is visited chiefly by native rubber-hunters, so that its char- 

 acteristics are very imperfectly known. Western Nicaragua, on the 

 other hand, is not heavily forested, and contains a relatively dense 

 population. For these and other reasons information concerning this 

 portion of the region is comparatively full. 



Topography 



general character of the topography 



The coramonl}^ accepted Humboldtian view of the topography of Cen- 

 tral America should be definitely discarded at the outset. According to 

 this view, which is still dominant in the text-books, a continuous moun- 

 tain chain connects the Cordilleran system of western North America with 

 the Andean system of western South America. Hill * has fully demon- 

 strated the falsit}^ of this old view and shown the complete independence 

 of the orographic systems of the three Americas. The due east-and-west 

 trend of the Central American mountain chains is perhaps less prevalent 

 than Hill has represented it. In the region under discussion, at least, 

 there is a distinct northwest-southeast trend in all the larger topographic 

 features. The same trend predominates in the geologic structures, and 

 the two are doubtless in some measure connected. The northwest-south- 

 east trend is observed in the ranges of volcanic peaks which cross the 

 isthmus diagonally from the Caribbean sea to the Pacific in northern 

 Costa Rica and western Nicaragua. It is also, though less distinctly, seen 

 in the Chontales hills between the Caribbean sea and the lakes, and again 

 in the great depression which extends diagonally across the isthmus be- 



* Robert T. Hill : Fundament9.1 Geographic Relations of three Americas, Nat. Geog. Mag., vol. 

 vii, 1896, pp. 175-181, 



