338 
ORIGIN OF LIFE IN AMERICA 
book form we are better able to appreciate the advances in our 
knowledge that are due to his investigations. His researches 
were not confined to recent zoology. He has also dealt with 
the subject from a palaeontological point of view, and has 
even subjected the main features of the flora to a detailed 
revision. All the same, he acknowledges that there are several 
important problems connected with the geological history of 
South America for which no satisfactory solution has as yet 
been suggested. More than twenty years ago, Dr. von Ihering 
announced that the close relationship of the Brazilian with 
the African fresh-water mussels implied the former existence 
of a land connection between South America and Africa.. 
But, whereas America as a whole is one of the richest regions 
for fresh-water mussels in the world, Chile and Peru are 
among the poorest. While east of the Andes there is a 
luxuriant fauna of fresh-water mussels largely related to that 
of Africa, we find only the genus Unio (in its wide sense) re¬ 
presented on the western slope of the mountains. Dr. von 
Ihering explains this and other similar facts by the supposi¬ 
tion that in the east and the west there were originally similar 
faunas, but while eastern South America obtained a rich stock 
of immigrants across the land bridge from Africa, the great 
mountain chain of the Andes, which was then commencing 
to rise, prevented any further influx westward. Considering 
that the fresh-water mussels (Unionidae) are well represented 
even in Jurassic deposits, Dr. von Ihering* recognised that the 
geographical distribution Of these mollusks may be utilised 
to advantage as indicators of very ancient, especially 
Mesozoic, conditions of land and water. 
In the course of his studies the same author came to the 
conclusion that from the Cretaceous to the end of the Pliocene 
Periods, South America must have been completely separated 
from North America. A real South American continent 
existed only since Oligocene times. It then consisted of two 
parts united by the narrow isthmus of the newly formed 
Andes. He named these two old original constituents of 
South America “ Archiguiana ” and “ Archiplata.” The 
former comprised the highlands of Guiana and Venezuela, 
* Ihering, H. von, “ Archhelenis and Archinotis,” p. 79. 
