542 



Arnold Heim- 



CoMONDXJ Formation.^ 



In some places the Isidro Formation is separated from the 

 overlying brown sandstones without unconformity, so that the 

 Comondu Formation might be regarded as the normal continuation 

 of sedimentation. In other localities, however, the Comondu 

 Formation is lying with a distinct angular unconformity upon the 

 Isidro Formation. 



The name Comondu is taken from the big oasis village, which is 

 situated at the bottom of a deep and narrow valley (map, Fig. 1), 

 the walls of which are formed of brownish sandstone and 

 conglomerate. These strata are nearly horizontal, and apparently 

 belong to the same formation as the beds which overlie the Isidro 

 Formation of La Purisima. At Comondu these sandstones and con- 

 glomerates are capped by basaltic lava of apparently the same 



N.W. 



S.E. 



Base line about 100 metres above sea-level. 



Fig. 4. — Section about 7 kilometres N.E. of Mission La Purisima. I. Isidro 

 Formation. C. Comondu Formation. M. In places quaternary con- 

 glomerate below basalt flow. B. Basalt lava flows, the south-eastern on 

 high mesa, the north-western on old terrace of Cadegomo Valley. L. Low 

 terrace conglomerate (later quaternary). 



character and age as that of La Purisima (Fig. 3, 4). The name of 

 Comondu Formation as applied for the region of La Purisima is 

 given with reserve, it being realized that this correlation has not yet 

 been proved with certainty. 



Taken as a whole, the Comondu Formation is composed of 

 brownish, sometimes concretionary sandstones, with beds of con- 

 glomerate. The pebbles are formed chiefly of basaltic rocks, also 

 tuff, sandstone, dioritic and granitic rocks. Toward the interior of 

 the Peninsula, in Cadegomo Valley, as well as in the Comondii 

 district, the sandstones pass into coarse conglomerates made up 

 chiefly of basaltic rocks. The high walls of the mountain 

 La Giganta (1,765 metres high) on the water-shed between 



^ " Braune Molasse," of the writer's paper, loc. cit., 1916. 



