“ANTONIO ALZATE.” 333 

The grey granites are similar to those which are found in various 
- portions of the republic and are the underlying or floor rock of the 
other formations. In Lower California they are extensively expored to 
the east of La Paz, and form a high mountain range (Cacachilas). On 
the line of the section under consideration they are traversed by nu- 
merous dykes of diorite. 
The granite conglomerate met with close to the eastern margin of 
the granite area, Í have not encountered in other localities. Lam, as yet 
unable to assign it to any horizon. 
The Crystaline slates.—These slates are unquestionably the oldest 
formation met with in Mexico after the granite, They are of the same 
formation found in Lower California, where they occur in synelinal 
basins and resting on the granite. The rock is schistose micaceous and 
the ore which occurs at the Triunfo and San Antonio mines (Lower 
California) occurs in beds or interitralified bodies. 
The gold ures of Placeres mines and many other localities occurs in 
this formation. The placer gold here occurs in the alluvial gravels rest- 
img on the granites. The extent of this founation is not as yet known, 
but there are enormously rich veins and placers distributed over a lar- 
ge area to the south and south east of the locality here cited. ' 
Lower Cretaceous.—The limestone which occurs at Coyuca unques- 
tionally belongs to the Necomian group as Prof. José G. Aguilera of 
the Geological Institute showed me specimens of Nerinea titanea (Fe- 
lix) found by bim at this locality. 
l am inclined to think that the silicious limestones pf San Gerónimo 
near Ajuchitlan also belong to this series. 
Section No. 3.—The line extends from the town of Pungarabato 
located just north of Coyuca, to the town of Huetamo, to the North 
and west. The Miocene breccia and red clay and slate of this group 
extend to the vicinity of Naranjo (ranch) where it is followed by olive 
slates, which extend to the base of the Mal Paso mountain which is a 
1 I have not visited other localities in this portion of the republic and there- 
¡Ore can not give any detail as 1o the formation. The origin ofthe placer gold is 
he crystaline slate iormation, 
