270 TlMEHRI. 
bably more corre6lly, attribute it to the action of glaciers 
in a former ice age. 
In Venezuela the name mocco de hierro is given to a 
highly ferruginous rock which assumes the various forms 
of 
a* Ferruginous conglomerate 
b. Ferruginous grit 
c. Ferruginous breccia 
d. Piso^itic brown iron-ore. 
It always consists mainly of limonite and earthy red 
haematite, with pebbles or angular and sub-angular frag- 
ments 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 mocco is found 
in loose blocks on the surface, and often forms plateaux 
of great extent which are generally marked by a bold 
rocky escarpment. This formation though frequently 
auriferous is not considered to afford evidence of quartz 
lodes in its immediate vicinity, as it is probably of alluvial 
origin and the quartz mines are generally situated at some 
little distance from it. In some cases the mocco is of 
undoubted alluvial origin, and the miners finding that 
when they met with a bed of mocco they usually had a 
good pay-dirt, came to the conclusion that the mocco 
was a good indication of gold deposits. The mocco has 
occasionally furnished nuggets covered with a black 
coating of oxide of iron, but while it is not uniformly 
payably auriferous in itself, it is probable that in many 
instances it may be found to overlie a pay-dirt or deposit 
of alluvial gold, and observations made on the similar 
formation in this colony appear to point to the same 
conclusion. 
