LINES OP ANCIENT WATEE LEVEL. 



57 



greater height than the pLaia generally ; there are, however, indications of lower water-level, 

 which are less extensive and less distinctly marked ; they occur in the north part of the valley, 

 and are disposed thus : The present river flows about four to six feet below its bank ; the 

 bottom of the river forms a small alluvial flat about a mile in breadth ; on each side of this a 

 higher plain, the more ancient bottom, extending for a mile on each side, and about twelve feet 

 higher than the true bottom ; this ancient bottom reaches to the foot of the mountain ranges. 

 Thirty feet high on the San Jose mountains a terrace is found, which may be traced for several • 

 miles north and south ; the line of this terrace is not horizontal, but apparently falls to the 

 southeast ; this may, however, be only apparent, as the level of the plain slopes in the opposite 

 direction. Opposite to this, near the camp at Quadre Domingo, the terrace on the sandstone of 

 the Santa Lucia is about the same height, and is covered with pebbles of red and green con- 

 glomerate, quartz, and porphyry. That on the San Jose is white clay and sand rock, in angular 

 fragments, with pebbles of the opalescent quartz found underlying the ostrea bed of Santa 

 Margarita ; above this terrace line is that one first described. The order of all these would be 

 thus: 



Total elevation above 

 sea, iu feet. 



Terrace 100—150 feet high on mountain. 



30 .do 



12 old river bottom 



— present bottom 



River.. 4 feet below 



1,690 

 1,542 

 1,512 

 1,500 



Plate 2, fig. 4, affords sections of these terrace levels, and an outline of the valley. 



8U 



