Perry.] 



72 [December 21» 



prevailed during the glacial period, a return of warmth was secured? 

 If the astronomic agencies already referred to be sufficient, when 

 taken in combination at their concurring points of greatest intensity, 

 to occasion a winter of the ages, the same agencies would be sure 

 to bring, in the natural course of things, an alternating seonian sum- 

 mer. This might be a long while in coming, and the glacial period 

 was probably of considerable duration ; still it must finally appear, 

 even as summer invariably succeeds to winter. 



Once more it is objected, that an ice-sheet moving southward 

 could not have produced the variations observable in the direction of 

 the strise. It seems to be forgotten by many that the glacial mass 

 must have varied in thickness during the different portions of the 

 ice-period. When it was at its acme, the direction, as a rule, must 

 have been north-southward. In the closing portion of the period, as 

 the thickness gradually diminished, the direction would be more 

 largely influenced by the inequalities of the country. Local glaciers 

 finally becoming predominant, their direction must be down the 

 existing valleys; thus in a great variety of directions, as in the Green 

 Mountains, predominantly east-west and west-east, leaving furrows 

 and grooves to correspond. Accordingly an ice-sheet, varying in 

 thickness at different stages, would produce just the variations 

 referred to, while they are hardly to be explained by resort to any 

 other known agency. 



The principal objections urged by Dr. Jackson having been con- 

 sidered, and, as it is thought, fairly met, the hypothesis proposed in 

 place of the glacier theory may be briefly noticed. 



And, first, some geologists have maintained that the effects, 

 referred to the agency of ice, were produced by the action of flowing 

 water. In respect to this hypothesis, it may be simply remarked that, 

 so far as we know, flowing water never produces, and is in no wise 

 able to produce, some of the most characteristic features of the 

 glacial times. In many cases the effects of its action are just the 

 opposite of those requiring an explanation. For instance, flowing 

 water tends to efface, not to produce, the polished surfaces met with 

 all over the country, whenever the underlying solid rock is freshly 

 laid bare. 



Again, and this is said to be the prevailing view, icebergs and ice- 

 floes are invoked as the all-sufficient cause of the phenomena. As 

 to the argument involved in "the prevailing view," he would simply 

 quote, "Broad is the way of delusion, and the many find it." To the 



