VOYAGE UP THE COAST TO PARA 147 



clearly marked, however, by an intervening bed of pebbles. 

 At Parahyba do Xorte the same sheet of drift, but con- 

 taining more and larger pebbles, rests above a decomposed 

 sandstone somewhat resembling the decomposed rock of 

 Pernambuco. In the undecomposed rock below, Mr. Ag- 

 assiz found some fossil shells. In the neighborhood of 

 Cape St. Roque we came upon sand-dunes resembling 

 those of Cape Cod, and wherever we sailed near enough 

 to the shore to see the banks distinctly, as was frequently 

 the case, the bed of drift below the shifting superficial 

 sands above was distinctly noticeable. The difference in 

 color between the white sand and the reddish soil beneath 

 made it easy to perceive their relations. At Ceara, where 

 we landed, Mr. Agassiz had an opportunity of satisfying 

 himself of this by closer examination. At Maranham 

 the drift is everywhere conspicuous, and at Para equally 

 so. This sheet of drift which he has thus followed from 

 Rio de Janeiro to the mouth of the Amazons is every- 

 where of the same geological constitution. It is always 

 a homogeneous clayey paste of a reddish color, containing 

 quartz pebbles ; and, whatever be the character of the rock 

 in place, whether granite, sandstone, gneiss, or lime, the 

 character of the drift never changes or partakes of that 

 of the rocks with which it is in contact. This certainly 

 proves that, whatever be its origin, it cannot be referred 

 to the localities where it is now found, but must have 

 been brought from a distance. Whoever shall track it 

 back to the place where this peculiar red soil with its 

 constituent elements forms the primitive rock, will have 

 solved the problem. I introduce here a letter written 

 by Mr. Agassiz, a few days later, to the Emperor, which 

 will better give his views on the subject. 



