CHAPTER II 



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 

 Piano de la Gobernation del Chubut, 1910, by A. Lefrancois. 

 This would be 45 io' 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, 



