400 



A JOURNEY IN BRAZIL. 



with the rock in place ; and also a bluff of this super- 

 ficial deposit studded with boulders, resting above the 

 partially stratified metamorphic rock.* Other excellent 

 opportunities for observing this formation, also within 

 easy reach fi^-om the city, are afforded along the whole 

 line of the Dc^ Pedro Segundo Railroad, where the 

 cuts expose admirable sections, showing the red, unstrat- 

 ified, homogeneous mass of sandy clay resting above the 

 solid rock, and often divided from it by a thin bed of 

 pebbles. There can be no doubt, in the mind of any 

 one familiar with similar facts observed in other parts of 

 the world, that this is one of the many forms of drift 

 connected with glacial action. I was, however, far from 

 anticipating, when I first met it in the neighborhood 

 of Rio, that I should afterwards find it spreading over 

 the surface of the country from north to south and from 

 east to west, with a continuity which gives legible 

 connection to the whole geological history of the con- 

 tinent. 



It is true that the extensive decomposition of the un- 

 derlying rock, penetrating sometimes to a considerable 

 depth, makes it often difficult to distinguish between it 

 and the drift; and the problem is made still more puz- 

 zling by the fact that the surface of the drift, when 

 baked by exposure to the hot sun, often assumes the 

 appearance of decomposed rock, so that great care is 

 required for a correct interpretation of the facts. A 

 little practice, however, trains the eye to read these ap- 

 pearances aright; and I may say that I have learned to 

 recognize everywhere the limit between the two forma- 

 tions. There is indeed one safe guide, namely, the un- 



* See Chapter III. p. 86. 



