PHYSICAL HISTOKY OF THE AMAZONS. 397 
CHAPTER XIII. 
PHYSICAL HISTORY OF THE AMAZONS. 
DRIFT ABOUT Rio DE JANEIRO. DECOMPOSITION OF UNDERLYING ROCK. 
DIFFERENT ASPECT OF GLACIAL, PHENOMENA IN DIFFERENT CONTINENTS. 
FERTILITY OF THE DRIFT. -- GEOLOGICAL OBSERVATIONS OF MESSRS. HARTT 
AND ST. JOHN. CORRESPONDENCE OF DEPOSITS ALONG THE COAST WITH 
THOSE OF RlO AND THOSE OF THE VALLEY OF THE AMAZONS. PRIMITIVE 
FORMATION OF THE VALLEY. FIRST KNOWN CHAPTER OF ITS HISTORY. 
CRETACEOUS FOSSIL FISHES. FORMER EXTENT OF THE SOUTH-AMERICAN 
COAST. CRETACEOUS FOSSILS FROM THE Rio PURUS. -- COMPARISON BE- 
TWEEN NORTH AND SOUTH AMERICA. GEOLOGICAL FORMATIONS ALONG 
THE BANKS OF THE AMAZONS. FOSSIL LEAVES. CLAYS AND SAND- 
STONES. HILLS OF ALMEYRIM. MONTE ALEGRE. SITUATION AND SCEN- 
ERY. SERRA ERERE. COMPARISON WITH Swiss SCENERY. BOULDERS OF 
ERERE. ANCIENT THICKNESS OF AMAZONIAN DEPOSITS. DIFFERENCE 
BETWEEN DRIFT OF THE AMAZONS AND THAT OF Rio. INFERENCES DRAWN 
FROM THE PRESENT CONDITION OF THE DEPOSITS. IMMENSE EXTENT OP 
SANDSTONE FORMATION. NATURE AND ORIGIN OF THESE DEPOSITS. RE- 
FERRED TO THE ICE-PERIOD. ABSENCE OF GLACIAL MARKS. GLACIAL 
EVIDENCE OF ANOTHER KIND. CHANGES IN THE OUTLINE OF THE SOUTH- 
AMERICAN COAST. SOURE. IGARAPE GRANDE. VIGIA. BAY OF BRA- 
GANZA. ANTICIPATION. 
A FEW days before we left Para, Senhor Pimenta Bueno 
invited his friends and acquaintances, who had expressed 
a wish to hear Mr. Agassiz's views on the geological char- 
acter of the Amazonian Valley, to meet at his house in 
the evening for that purpose. The guests were some two 
hundred in number, and the whole affair was very uncere- 
monious, assuming rather the character of a meeting for 

conversation or discussion than that of an audience col- 
lected to hear a studied address. The substance of this 
talk or lecture, as subsequently written out by Mr. Agassiz, 
afterward appeared in the Atlantic Monthly, and is in- 
serted here, with some few alterations under the head 
