CHAPRER TT 
AGE OF THE DESEADO FORMATION 
THE locality worked by the Amherst party is situated 
about three miles east of the Chico River, just across the 
line of the homestead of D. J. Venter as plotted on the 
Plano de la Gobernation del Chubut, 1910, by A. Lefrancois. 
This would be 45° 10’ S., and 67° 32’ W. (or as on the map 
9° 15’ W. of the meridian of Buenos Aires). The exposure 
is on all sides of an elongated hill about a sixth of a mile 
long, averaging 200 feet wide, and constricted in the middle 
to a narrow neck. Figure 2 shows a section of the hill, 
made along the north side, and indicates the varied charac- 
ter of the stratified deposits. 
The material varies from brown sandy clay shales, to 
yellow sandy clay with concretions, and is capped with a 
varying layer of greenish sand, which, in some places, is 
coarse and irregular, in others fine and uniform, and in 
still other places is mixed with considerable quantities of 
volcanic ash. In it are many mud balls and also bits of 
bone which have been worn round, others but slightly 
worn, and finally bones and skeletons which apparently 
have been buried where they fell. “This green sand is mostly 
covered with a layer of two feet of hard sandstone of the 
same composition as the rest of the bed, but cemented 
into a dense layer. Above the green sand is a layer of 
fine grey sand, prettily crossbedded, and of varying thick- 
ness, but without fossils. Remains of vertebrate animals 
occurred in the brown clay, the yellow clay and the green 
sand, and in all the cases fossils were of unusual abundance 
so that in this limited locality we collected over 300 speci- 
mens. 
Above the Deseado (layers 2 to 5) lies the Patagonian 
in its typical development, filled with Ostrea ingens, 
