DETRITIC FORMAT IONS 89 
; on great fault walls. The strata are tilted here in many directions. 
To the south of the Pagancillo lowland we meet with the great 
sandstone terrane of the Campo de Talampaya, consisting, accor- 
ding to Bodenbender’s map (1911), of cretaceous beds. 
b) SUMMARY OF THE STRATIGRAPHY. 
i Above is characterized the lithological habit and the mutual rela- 
tions of the continental strata, covering the old crystalline rocks. 
| An attempt to arrange these strata into a chronological succession 
from the base to the top and a trial to separate some greater sedi- 
mentary divisions and to determine their age may be convenient. 
By, the almost complete absence of fossils this task will naturally 
obe only a very approximative one, based, as it is, on the lithologi- 
cal and tectonical peculiarities, and to some degree on the beha- 
viour of the divisions to these in the surrounding regions. 
The first question considering the age of the continental strata 
is that of the age of the basal plane. In other words: how old is 
the cutting plane in the Umango crystalline basement, supporting 
all the clastic continental rocks and their effusives? 
In the province of La Rioja aside from the Cordilleran chain 
there is a considerable number of known occurrences of plant- 
bearing lower Gondwana strata, forming the basal layers of the 
continental series and lying with a great unconformity over the 
steeply inclined and mostly granite intruded crystalline schists. The 
lower Gondwana occurrences, consisting of yellowish and gray 
sandstones with coal seams and often’ with a basal conglomerate, 
are: 
1. Cerro Bola. 
2. Cerro Villa Union (Cerro Guandacol, profile descr. page 68). 
' 3. Nevado de Famatina: 
a) Quebrada de Tambillos. 
b) Carrizal. 
c) Potrero de los Angulos. 
