GEOMORPHOLOGY 127 
along the eastern slope of the Sierra de Umango ridge a few rem- 
nants of gravel covered plains more than a hundred meters over 
the valley bottoms (Quebrada Espinal). — To the east of Villa 
Union, near to the extreme foot of the Nevado de Famatina there 
are also remnants of older plains appearing in the form of well 
marked terraces (Puerto Alegre). Some lower terraces farther out 
in the lowland are of considerable extensions. They all slope west- 
_ ward from the Nevado. In former times they have probably exten- 
ded over the greater part of the Pagancillo lowland. The Lomas de 
Villa Union are but the last withnesses of these plains. Every hill 
here has a flat summit covered with a gravel sheet (old sheet flood 
plain). 
The best preserved sheet flood cones are, of course, those of 
younger date (later quaternary?). They, indeed, form almost all lower 
slopes of the existing mountains. The best developed ones occur 
on the eastern slope of the Cerro Potrero Viejo (toward the open 
Vinchina valley). Also the cones on the western side of the Cerro 
Villa Union (the Guandacol valley) are of wide extension. Giant 
cones have developed also along the western margin of the Nevado 
de Famatina. 
Recent sheet flood cones seem not to be deveioped, because 
the last erosion phase, as will be stated below, has only worked 
by linear way, cutting through the cones and forming canyonlike 
gorges. The main cones correspond to the main valleys, and the 
main features of the sculpture seem to have been formed during 
the last phase of sheet flooding. . 
3) A later (recent) erosion phase. Linear cutting. 
Riversterraees. 
On studying the great sheet flood cones and their corresponding 
valleys one finds, that these forms have been to a high degree 
modified by a erosion, caused by an subrecent uplift of the moun- 
tains (or by a relative sinking of the valley floors.) This later phase 
