VOYAGE FROM NEW YORK TO RIO DE JANEIRO. 17 
If this be correct, it is very inconsistent with what we know 
of the geological structure of other continents, where the 
stratified rocks are in much larger proportions." 
Upon this followed some account of the different kinds of 
valley formation and of terraces. " Do the old terraces 
above the rivers of South America correspond to the river 
terraces on any of our rivers, those of the Connecticut, 
for instance, showing that their waters had formerly a 
much greater depth and covered a much wider bottom ? 
There must of course have been a cause for this great 
accumulation of water in ancient periods. I account for it 
in the northern half of the hemisphere by the melting of 
vast masses of ice in the glacial period, causing immense 
freshets. There is no trustworthy account of the river 
terraces in Brazil. Bates, however, describes flat-topped 
hills between Santarem and Para in the narrow part of the 
valley, near Almeyrim, rising 800 feet above the present 
level of the Amazons. If this part of the valley were 
flooded in old times, banks might have been formed of which 
these hills are a remnant. But because such a theory 
might account for the facts it does not follow that the 
theory is true. Our work must be to study the facts, to 
see, among other tilings, of what these hills are built, 
whether of rock or of loose materials. No one has told 
us anything as yet of their geological constitution." 
To-day we have seen numbers of flying-fish from the 
deck and were astonished at the grace and beauty of their 
motion, which we had supposed to be rather a leap than 
actual flight. And flight indeed it is not, their pectoral 
* Mr. Agassiz afterward visited these hills himself, and an account of their 
structure and probable origin will be found in the chapter on the physical 
history of the Amazons. 
2 
