SUPPOSED GLACIATION OF BRAZIL. 765 



depth of fifteen feet or more with clays, through which are min- 

 gled boulders of diorite and granite and fragments of quartz. 

 Further east, at a lower level, some of the clays have been washed 

 over and contain subangular fragments of quartz, some of them 

 two feet in diameter, many of which are somewhat water-worn. 

 It is perhaps worth mentioning that these water-worn quartz 

 fragments imbedded in clays were regarded by Hartt as the best 

 evidence of glaciation. They were finally eliminated as such 

 evidence near the end of a rainy season by my finding a land- 

 slide filling up a small ravine in which the bed of the stream had 

 been strewn with similar quartz fragments, and the whole buried 

 beneath a slide of crumpled clays. A highly instructive lesson 

 can be had on the subject of boulders and clays, their origin and 

 relations to the so-called drift of Brazil from Professor Derby's 

 paper on nephelene rocks in Brazil. 1 Anyone reading that 

 article can readily fancy how Professor Agassiz, in a flying trip 

 across Sao Paulo and Minas, would have interpreted these clays 

 and boulders of different kinds and different colors. 



In regard to the so-called erratics I should mention also the 

 opinion of another observer and writer upon Brazilian geology. 

 Emmanuel Liais, formerly director of the Imperial Observatory at 

 Rio de Janeiro, is very positive that there are no evidences what- 

 ever of glaciation in Brazil. Of the boulders supposed to be 

 erratics, he says : 2 



" These boulders though numerous are always in the immediate neighbor- 

 hood of the veins from which they are derived Though presenting 



sometimes the appearance of erratics by their abundance and rectilinear 

 arrangement, they are not transported boulders, and have nothing in common 



•with erratic phenomena I have not been able to find any signs of the 



existence of a boulder that can be regarded as erratic and coming from a 

 region distant from the one where it is found. In the vicinity of these isolated 

 boulders one always finds dikes, veins or simply masses or boulders of the 

 same material intercalated with the terrain in place." 



He speaks of the occurrence of dikes of diorite from which 

 many of the boulders cited by Agassiz have been derived. More 



J Quar. Jour. Geol. Soc, 1887, XLIIL, 457-473. 

 2 Climats, Geologie, etc., du Bresil, Paris, 1872, 18. 



