H liRSHEY.] 



Isthmus of Panama. 



253 



Los Saltos. Tlie valleys are merely deep, narrow, steep-sided 

 ditches carved from the plateau by the streams. Eliminating them, 

 the whole country over a width of about 20 or 25 miles would be a 

 high plateau, arched a little along the central line, but otherwise 

 remarkably even. 



Upon first recognizing the existence of this uplifted and dissected 

 plain, I attributed it to the original constructional surface, but a 

 little reflection showed this to be untenable. The volcanic cones, 

 craters, and other causes of unevenness in the original surface have 

 disappeared over the cordilleran region. Even the Panama tuffs so 

 well represented in the foot-hills on the south of the high sierra, 

 and which must have lapped over onto this region, have been com- 

 pletely removed. 



To my mind the most unanswerable argument in favor of the 

 idea of great erosion over the Veraguas Mountain belt is in the 

 fact that at places the syenite rises to the level of the old plain. 

 This coarse crystalline certainly did not solidify at or very near the 

 surface, but must have been buried under a considerable mass of 

 other rocks. Moreover, the "higher" strata are absent on the 

 north side of the mountains along the coast of the Caribbean Sea. 

 On the whole, I consider the evidence of erosion over the cor- 

 dilleran region to form the ancient plain of the sierra summits 

 sufficiently strong to make it practically a demonstration. 



Between the Aguadulce-Santiago plain and the high sierra is 

 a belt of lower mountains or montanas, 10 to 20 miles in width. 

 It is made up of separate ridges trending in various directions, 

 and of isolated peaks. At first sight the whole seems to be an 

 unsystematic collection of steep-sided and narrow-crested hills of 

 various heights; but from certain advantageous points of view the 

 impression is forced on the observer that if a plane were drawn from 

 the edge of the dissected plateau over the cordillera to the summit 

 plane of the monadnocks on the low plain, many of the summits of 

 the foot-hills would fall in this plane and none above it. Where 

 erosion has been very active in this belt, the ridges have been 

 reduced below the old plain surface, but the bulkier ones with com- 

 paratively even crests, and the larger isolated peaks form a sloping, 

 dissected plain almost as perfectly as do the monadnocks below. 



