5 UPPOSED GLA CIA TION OF BRA ZIL. 7 $9 



(p. 272) he speaks of having traced the palpable evidence of 

 glaciation "from Montevideo on the Atlantic to Talcahuano on 

 the Pacific coast." Speaking of evidence at Concepcion Bay he 

 says also (p. 272) "Think of it! A characteristic surface indicat- 

 ing glacial action in latitude 37 S. at the level of the sea!" 



These quotations show as plainly as anything short of a pos- 

 itive statement can that Agassiz in 1872 no longer considered as 

 trustworthy what he had formerly regarded as the evidences of 

 glaciation in Brazil. For if he still believed in a glacier under 

 the equator itself, why should he tell us with exclamation points 

 to think of a glacier thirty-seven degrees nearer the pole ? 



BASIS OF THE THEORY. 



I should be glad to leave the matter with these statements of 

 the changes of views on the part of both advocates of the glacia- 

 tion of Brazil, but persons who have theories based to a greater 

 or less extent on the glaciation of the tropics are very reluctant 

 to believe, in the face of the many positive statements of both 

 Agassiz and Hartt, and of the apparently trustworthy evidence 

 adduced by them, that the first impressions of those excellent 

 observers, both of whom were thoroughly familiar with glacial 

 phenomena in the north, were altogether wrong. It is not possi- 

 ble, neither is it necessary, to take up here the individual cases 

 spoken of by Agassiz and Hartt as evidence of glacial action. 

 Very nearly all the materials referred by them to the drift fall 

 under two principal heads : 



First, the so-called erratic boulders, often imbedded in what 

 was considered boulder-clay. 



Second, transported, water- worn materials. 



ORIGIN OF THE BOULDERS. 



The boulders believed to be erratics are not erratics in the 

 sense implied, though they are not always in place. The first 

 and most common are boulders of decomposition, either rounded 

 or subangular, left by the decay of granite or gneiss. Some- 

 times they are imbedded in residuary, and consequently unstrati- 



