16 



ANNALS NEW YORK ACADE3IY OF SCIENCES 



This type of topography is represented by the small level tract surrounded 

 or dotted over with small hills, called "pepino hills" locally, standing 

 like haystacks above the plain at many different elevations above the sea. 

 This leads to the belief that the fundamental control in its development 

 is the presence of a shaly bed in the series, which forms at each point the 

 basis of the local plain. The hillocks standing above it or surrounding 

 it represent remnants of the more massive and probably more porous and 

 more easily destroyed limestone which has been attacked and largely 

 removed liv weathering, and especially by solution, down to the more 



■**W"*|p.'- 



Fig. :i. — V neon foniii III ieloiv Ike Arecibn luniuii khi 



This view sliows llie older iilt('<l ;iii(l ei-dded tuffs and sliales lielow, as seen on the 

 Arecibo Uiver. The contact is iiumediatel.y l)eneaih the horizontally bedded limestones at 

 about the center of the view whei-e the chief weatheriua is noted. 



resistant shaly suii-furming nieinbcr. If tliis is the principal cause of 

 the peculiar topographic form just described, it is quite easy to see that 

 the distrilnition of such features should be expected to be rather irregular 

 both in lateral extent and in actual elevation above sea level or in rela- 

 tion to ilu! different horizons in the formation itself. In regarding this 

 as the principal factor, there is no tendency to overlook the fact that the 

 island lias stood at different elevations with rcs])cet to sea level in former 

 times, and that a corresponding difference in ground water levels would 

 be folt tlirougliont the border resion. But tliere is no evidence whatever 



