EXCURSIONS ON THE COAST. 387 
of its surface, is the well-known reddish sandy clay, with 
quartz pebbles scattered through its mass, and only here 
and there faint traces of an indistinct stratification. This 
afternoon Mr. Agassiz has been again on shore, examining 
the formation of both banks of the Igarape Grande, the 
river at the mouth of which stands the town of Soures. 
He has returned delighted with the result of his day's 
work, having not only obtained the most complete evidence 
that the geological formation of Marajo corresponds ex- 
actly with that of the Amazonian Valley, but having also 
obtained some very important data with respect to the 
present encroachments of the sea upon the shore. He 
found upon the beach, partially covered by sea-sand, the 
remains of a forest which evidently grew in a peat-bog, and 
which the ocean is gradually laying bare. 
February 2th. Early this morning we crossed the Para. 
River, and anchored at the entrance of the bay within which 
stands the town of Yigia. We landed, and while the boat- 
men were dragging the net, we wandered along the beach, 
which is bordered by thick forest, now full of flowers. Here 
we found the same geological formations as on the Marajo 
shore, and on the beach the counterpart of the ancient for- 
est which Mr. Agassiz unearthed yesterday on the opposite 
coast. There can hardly be more convincing evidence that 
the rivers which empty into the Amazons near its mouth, 
like all those higher up, as well as the main stream itself, 
have cut their way through identical formations, which 
were once continuous. Evidently these remains of forests 
on the beaches of Vigia Bay and at the mouth of the Iga- 
rape Grande are parts of one forest, formerly uninterrupted 
and covering the whole of the intervening space now filled 
by the so-called Pard River. We followed the beach to the 
