VALLEY OF THE AMAZONS. 
163 
tion, has been making collections and geologi¬ 
cal observations in the province of Spiritu 
Santo, in the valley of the Rio Doce, and 
afterwards in the valley of the Mucnry. He 
informs me that be lias found everywhere the 
same sheet of red, unstratified clay, with peb¬ 
bles and occasional boulders, overlying the 
rock in place. Mr. Orestes St. John, who, 
taking the road through the interior, has vis¬ 
ited, with the same objects in view, the valleys 
of the Rio San Francisco and the Rio das Vel- 
has, and also the valley of Piauhy, gives the 
same account, with the exception that he 
found no erratic boulders in these more north¬ 
ern regions. The rarity of erratic boulders, 
not only in the deposits of the Amazons proper, 
but in those of the whole region which may be 
considered as the Amazonian basin, is account¬ 
ed for, as we shall see hereafter, by the mode 
of their formation. The observations of Mr. 
Hartt and Mr. St. John are the more valuable, 
because I had employed them both, on our 
first arrival in Rio, in making geological sur¬ 
veys of different sections on the Dom Pedro 
Railroad, so that they had a great familiarity 
with those formations before starting on their 
