Page:The Journal of geology (IA journalofgeology11893univers).pdf/337

(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 indicating glacial action in latitude 37° S. at the level of the sea!"

These quotations show as plainly as anything short of a positive 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 thiry-seven degrees nearer the pole?

I should be glad to leave the matter with these statements of the changes of views on the part of both advocates of the glaciation 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 possible, 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.

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. Sometimes they are imbedded in residuary, and consequently unstrati-