STRATIGRAPHICAL GEOLOGY 
419 
various colored marls and dark , clays with boulders, gravel, and 
dinosaur bones; fossil wood, and plant remains are quite abund¬ 
ant. Glauconitic green and brown sandstone was deposited at the 
close of the Cretacic time, upon which lie unconformably the 
marine Tertic sediments. 
The author attributes ^ the change in the character of the con¬ 
tinental deposition to either a change in the manner of weathering 
in the denudation district or to an entirely new source of material. 
The latter seems improbable. The sandstone at the base is the 
result of mechanical disintegration in an arid or semi-arid climate, 
while the clays and marls are the result of chemical weathering 
under the influence of a more humid climate. Mechanical weath¬ 
ering has its maximum development in areas where there is much 
frost and rapid temperature changes. The climate would not be 
especially favorable for vegetation, although observation has 
shown that it was not entirely lacking. The dinosaur bones are 
found almost exclusively in the upper member. A moist climate 
is supposed to have prevailed at that time. 
This group of strata is similar in its genetic relations to the Old 
Red sandstone of England, the Red Beds of North America, the 
Permo-Carboniferous sandstones of the Karroo formation of 
Africa, a single member of the German Triassic section, our wes¬ 
tern Morrisonian series, and the desert sandstones of Australia. 
Especially is this combination of strata in Patagonia comparable 
with the Nubian sandstones of North Africa, with which it cor¬ 
responds not only in general lithologic relations, but also in having 
a marine transgression in its upper part. 
From a critical study of Late Cretacic sedimentation, there is 
established certain areas along the Atlantic coast which are con¬ 
sidered negative elements or depression areas. These areas repre¬ 
sent the interior of ancient mountain arcs. The lateral move¬ 
ments of Permian age as Keidel observed them in the southern 
Sierras of Buenos Aires and in the Pre-Cordillera, extend in the 
form of an open arc against the Brasilian shield. It is believed 
that these arcs represent the maximum development, probably, of 
a force that was in action farther south, although in the present 
state of knowledge these extensions cannot be proved. However, 
the movements must have been influenced by the geosyncline be- 
1 Ein Blick auf Schichtenfolge und Gebirgsbau im sudlichen Patagonien: Geol. 
Rundschau, iii Bd., hft. 3, pp. 109-137, 1921. 
