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 Igarapd Grande, the 

 river at the mouth of which stands the town of Soure's. 

 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 29th. 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- 

 rap Grande are parts of one forest, formerly uninterrupted 

 and covering the whole of the intervening space now filled 

 by the so-called Pani River. We followed the beach to the 



