1869.] LE NEYE FOSTER CARATAL G-OLD-FIELD. 341 



there is a layer of red earth, often containing pieces of auriferous vein- 

 quartz, pieces of " moco de hierro " and grains of pisolitic brown 

 haematite, the " granson " of the miners. When washed, this 

 " tierra de flor," or '^' surface earth," as it is caUed, furnishes, in 

 addition, decomposed crystals of iron pyrites, a black magnetic iron 

 sand called " arenilla," and often nuggets of gold. The manner in 

 which the gold occurs appears to be very irregular ; the miner may 

 wash "batea" after "batea" of earth and find no gold, or only the 

 " color de oro" {i. e. merely a few fine grains of gold), and then get 

 several nuggets in the next lot. The largest nugget yet found in 

 the Caratal district was obtained from the " tierra de flor," close to 

 Nueva Providencia ; it weighed 15 lbs. 



In the diggings at the south-south-west corner of the town I saw 

 " tierra de flor " lying above alluvial ground. 



The following is the succession : — 



1. Soil. 



2. " Tierra de flor," red earth, with loose stones of quartz. 



3. Ferruginous clay. 



4. " Greda," or pay-dirt, yellowish clay, with blocks of quartz. 



5. " Cascajo," or bed-rock, decomposed schist. 



From the manner in which this " tierra de flor " occurred, I at 

 once concluded that, geologically speaking, it was a "rainwash;" 

 but it was some time before I understood whence it was immediately 

 derived. At last, after talking the matter over very frequently, 

 Dr. Plassard and I arrived at the conclusion that the " tierra de 

 flor" is nothing more or less than decomposed " moco de hierro " 

 washed down the hillsides. 



The name ^' moco de hierro " is given to a highly ferruginous, 

 rock, which assumes the vaiious forms of: — 

 a. Ferruginous conglomerate. 

 h. Ferruginous grit. 



c. Ferruginous breccia. 



d, Pisolitic brown iron-ore. 



It always consists mainly of limonite and earthy red haematite, 

 with pebbles or angular and subangular fragments of quartz, schist, 

 and felstone. When it takes the form of pisolitic brown iron-ore, it 

 consists of a number of globular concretions of limonite. This 

 "moco" is found in loose blocks on the surface, and often forms 

 plateaux, sometimes more than a hundred (or even two hundred) 

 acres in extent. The edge of the plateau is generally marked by a 

 bold rocky escarpment. Here it may be seen that the " moco " is 

 6, 8, or even 10 feet thick at the least ; and the same thing may be 

 observed where a stream has cut its way down through a " moco " 

 plateau as shown in fig. 4. 



In searching for quartz-lodes I came to the conclusion that the 

 " moco de hierro " aifords no evidence of lodes in the immediate 

 vicinity ; for my observations led me to infer that it is probably of 

 alluvial origin. I should suppose that the ferruginous matter of 

 which it consists so largely is derived from iron pyrites, which was 



