390 A JOURNEY IN BRAZIL. 
during the last eighteen or twenty years, the beach had re- 
ceded considerably in some places ; the high-water line being 
many yards beyond its former limit. The result of this ex- 
cursion has shown that, with the exception of some low mud- 
islands nearly level with the water, all the harbor islands 
lying in the mouth of the Amazons are, geologically 
speaking, parts of the Amazonian Valley, having the same 
structure. They were, no doubt, formerly continuous 
with the shore, but are separated now, partly by the fresh 
waters cutting their way through the land to the ocean, 
partly by the progress of the sea itself. 
March 2th. - - Our quiet life at Nazareth, though full of 
enjoyment for tired travellers, affords little material for a 
journal. A second excursion along the coast has furnished 
Mr. Agassiz with new evidence of the rapid changes in the 
outline of the shore, produced by the encroachment of the 
sea. So fast is this going on that some of the public works 
near the coast are already endangered by the advance of 
the ocean upon the land. During the past week he has 
been especially occupied in directing the work of a photo- 
graphist employed by Senhor Pimenta Bueno, who, with his 
usual liberality towards the scientific objects of the expedi- 
tion, is collecting in this way the portraits of some remark- 
able palms and other trees about his house and grounds. 
One of the most striking is a huge Sumaumera, with but- 
tressed trunk. These buttresses start at a distance of about 
eight or ten feet from the ground, spreading gradually to- 
ward the base ; they are from ten to twelve feet in depth. 
The lower part of the trunk is thus divided into open com- 
partments, sometimes so large that two or three persons can 
stand within them. This disposition to throw out flanks or 
wings is not confined to one kind of tree, but occurs in 
