Occasional Papers of the Museum of Zoology 9 



rocks, such as diabase, quartz-diorite (northem Aruba) and 

 mica-porphyrite (northern Bonaire). These older rocks may 

 resist erosion so as to form the highest hills in the islands (figs. 

 iii-6, and vi-14), or they may be peneplainized (especially 

 the diabase) to rolling plains (fig. vii-17), inside of the lime- 

 stone ramparts (fig. iii-5) along the seashore. Most of the soil 

 of the islands is derived from these more ancient rocks, but the 

 rapid erosion prevents the retention of much residue, except 

 on the more nearly level portions. As a result, almost all of 

 the agricultural development (hofjes), except the aloe plan- 

 tations, is in the valleys of these central basins. 



The calcareous strata are markedly unconformable on the 

 older rocks. The earlier limestone layers are very hard and 

 are darker in color; the more recent ones (fig. iii-7) are simply 

 exposed coral reefs and are quite soft and chalky in texture. 

 "Where exposed, the older limestone (fig. vi-14) erodes into 

 characteristic jagged points, separated by irregularly rounded 

 holes, which may be several feet in depth; thin slabs of this 

 material ring like steel when struck. The central dome has 

 been largely removed, but in the middle of Curacao and on 

 the southern ends of Aruba and Bonaire, the calcareous rocks 

 still practically bridge each island, while capped monadnocks, 

 such as the Tafelberg of Sint Hyronimus (PI. I, Curasao, 

 20-N) and Ronde Klip (12-P) on Curasao, show its former 

 extent and altitude. Usually the southwestern rim is more 

 markedly tilted than the northeastern; the latter is often 

 eroded almost to the shore (northern Curasao and Aruba), or 

 may remain as flat-topped ridges and mesas of the older lime- 

 stone (for example, the coast of Hato, Curacao; fig. v-13), 

 while the former is carved by the canyon-like valley outlets 

 into bold, angular hills (fig. iii-5). ^° Almost invariably, the 

 northeastern escarpments of all of the older remnants form 

 vertical, or even overhanging cliffs, which are commonly exca- 

 vated into more or less extensive caves, and decorated with 



10 K. Martin, I, Plate IX, shows the iuland side of the limestone rim 

 from Seroe Domi to Seroe Salinja Abau, with the Tafelberg of Santa 

 Barbara in the background. 



