210 THE FUTURE OF ARID LANDS 
4 
Figure 6. Watergap carved by the Jaguaribe River through steeply 
dipping quartzite beds of the Serra dos Orés. 
a beneficial effect on the climate of the area (3). Although no 
proof is presented, the existence of these lakes is unquestioned 
among those responsible for the plans formulated and put into 
operation in the Nordeste. 
To anyone familiar with the study of landforms, evidence that 
extensive sedimentary strata blanketed the crystalline undermass 
in late Tertiary times suggests an entirely different origin for the 
watergaps. This interpretation may be outlined as follows. The 
drainage system, freshly initiated upon the unbroken sedimentary 
covering, conformed to the surface irregularities of the stratified 
beds, being, of course, entirely independent of the topography and 
structure of the buried crystalline base. In time, the streams cut 
into the underlying basement and sawed across the buried ranges, 
from which the covering was ultimately stripped (Figure 7). 
It is true that whatever their origin may be, the gorges generally 
provide good dam sites. Their abundance, however, hardly justi- 
fies the description of this region as “‘the ideal land for the con- 
struction of reservoirs” (5). In fact, areas of adequate topography 
for large storage systems are not plentiful. In the absence of 
indispensable technical studies, the notion that they were to take 
the place of former lakes may have contributed to the premature 
establishment of some large scale reservoirs. In challenging the 
lake theory, the physiographer does not pretend that his broad 
interpretations are a substitute for detailed engineering studies, 
but they might contribute to avoid construction of dams, before 
