Limestone towers, residual hills occurring in northern Puerto Rico, between Arecibo and Manati, have been examined by field investigation and photogrammetry. Previously, these landforms have been described only qualitatively; in this paper summit densities, heights, diameters, planimetric shapes, and orientations are quantified.
Tower heights are generally less than 25 m; diameters range from 10 to 200 m. Diameter/height ratios range from 1.42 to 7.50. These values place the hills in the Sewu class of Balazs' (1971) classification of tropical karst styles. Towers are predominantly elongate in plan view, and pronounced long-axis orientations are evident. Tower summits exhibit a distribution that approaches uniformity.
The relationship between the residual hills and the adjacent cockpit karst area indicates a similar origin for both areas, with differences in summit densities relating to the distribution of surficial deposits, which promote subsurface corrasion. Tower slope asymmetry occurs only in 35% of cases, and it is probably related to basal erosion, induration of the limestone surface being of secondary importance.