1870.] 73 [Perry. 



hypothesis itself he could only devote a word. That bergs from an 

 arctic continent did not bring the drift, is evident from the fact that it 

 was to a large extent derived from rocks lying only a short distance 

 to the north of the respective places in which it is now found. It is 

 equally clear that the great mass of typical drift was not formed by 

 local glaciers, since it spreads in one continuous sheet, having com- 

 mon glacial characteristics, over the whole region, while it is itself in 

 places uncomformably overlaid by the debris of local ice-streams. 

 That it was not dropped by slowly-thawing icebergs, either as 

 stranded or in motion, is also apparent, since matter thus disengaged 

 would fall particle by particle and be regularly arranged or semi- 

 stratified, and not left in a jumble. So it is manifest that icebergs 

 did not erode, polish and striate almost the whole rocky floor of the 

 country, since the drift markings are made obliquely across meridional 

 ridges, ordinarily without the slightest reference to differences of 

 level. Indeed, for icebergs to make continuous furrows over high 

 hills and through deep intervening valleys, irrespective of the ever- 

 varying inequalities of surface, would be a far greater marvel than 

 the wonders to be explained. 



Having thus discussed some of the objections to the glacier theory 

 and having briefly shown why he had never been able to adopt the 

 iceberg hypothesis, he desired to bear witness to the great number and 

 accuracy of Dr. Jackson's observations of drift phenomena, and to 

 assure him of his kindest personal regard. 



After Rev. Mr. Perry's answer, Dr. Jackson said that Mr. Perry 

 had made an excellent defence of the glacial theory, but had not 

 removed his objections. He did not see how volcanoes, in distant 

 countries, could furnish the moisture required for the production of 

 thousands of feet of ice in New England, nor could he understand 

 how a glacier could rise from the bottom of Lake Superior, which is 

 more than six hundred feet below the sea level, or how glaciers could 

 exist in Brazil. 



To the additional objections suggested by Dr. Jackson, Mr. 

 Perry briefly replied. 



As to the statement that, however effective volcanic agency may 

 have been elsewhere, at the close of the tertiary period, it could have 

 had little influence in New England, since there were no volcanoes 



