340 



PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. [JuDO 9, 



formation obtained from Dr. Plassard, who was at Caratal while 

 this stuff was being worked. 



Fig. 3. — /Section of Alluvial Digging near Nueva Providencia. 



24-ft :-:: 



The following is the succession of the beds : — 



1. Soil. 



2. Red clay, showing no signs of stratification. 



3. Soft clayey " moco de hierro." 



4. Hard " moco de hierro," brown iron ore, with pieces of quartz 

 in it and a httle clay. 



5. Blocks of vein-quartz, often auriferous. 



6. "Greda," or pay-dirt, a yellow ferruginons clay containing 

 nuggets and small grains of gold. 



7. " Cascajo," decomposed schist, forming the " bed-rock." 



About half a mile from the town, on the road to Tupuquen, are 

 the " Planada" diggings, said to have been worked with much profit 

 in 1857. The section of one of the Planada pits is as follows : — 



1. Soil. 



2. Clayey gravel. 



3. Blocks of quartz. 



4. " Greda," or pay-dirt. 



5. " Cascajo," the bed-rock. 



In a neighbouring pit I saw about 6 feet of clay and then 6 feet 

 of gravel, the bottom being filled with rubbish. The pebbles found 

 in the gravel are mainly composed of the greenish grey felstone, 

 known as " piedra negra ; " subangular and rounded pieces of ferru- 

 ginons hornstone are also common. Higher up the valleys the placer 

 diggings are shallower. 



3. Tierra de Flor and Moco de Hierro. — In many places in the 

 Caratal district, just below the soil, at a depth of 18 inches to 3 feet, 



