THEORY. 191 



shape of beaches and terraces, while it may be that icebergs and glaciers modified the 

 whole. It may be too that paroxysmal movements occasionally accelerated, retarded or 

 modified, the effects. The period over which the uninterrupted operation of these agen- 

 cies can be traced, may be regarded as the alluvial, and we can refer them back at least 

 to the tertiary epoch. 



THE HISTORIC PERIOD. 



We arc now brought to the period when the country had attained essentially its present 

 altitude, the period of the later terraces and of man. All the agencies that produced drift, 

 namely, icebergs, glaciers, land-slips and waves of translation, are still in operation in 

 some parts of the world, and therefore real drift is still being produced. Ever since the 

 tertiary period, these causes have been acting ; but their intensity has varied in different 



ages. 



The same is true of the agencies that have produced beaches, osars, escars, moraine 

 terraces, marl beds, peat bogs, and deposits from springs, namely : the action of rivers 

 and the ocean, combined with the secular elevation of continents. In other words, the 

 agencies producing drift and modified drift have run parallel to each other from the very 

 first. Hence they both are varieties of the same formation, extending from the close 

 of the tertiary period to the present. 



Man has existed upon the earth a comparatively short part of the Alluvial Period. 

 We have a few records of the commencement of the modified drift, in cases of old river 

 beds upon a former continent, which will be described in another part of the Report. 

 The fossil Elephant from Mount Holly, and the Cetacean from Charlotte, and the littoral 

 shells of the Champlain clays may have been coeval with man, though we have no reliable 

 historic accounts of them, and probably they were vastly earlier. 



[BY E. H., SENIOR.] 



We introduce here, as perhaps the most appropriate place, an account of two quite 

 anomalous phenomena which have fallen under our notice in the Modified Drift of 

 Vermont. All geologists may not agree with our explanations : But we give the best that 

 occur to us. 



LAKE RAMPARTS. 



A few years ago the newspapers contained an account of certain walls of rounded stones, 

 lining the margin of some of the smaller lakes in Iowa, and which were supposed to be 

 the work of man. One of our number suggested in the papers, without having seen 

 them, that they were probably the work of ice ; but we did not dream of finding the 

 same phenomena in Vermont. Yet as we were exploring the shores of Willoughby Lake, 

 we found the same thing on its northeast side, by the road to Brownington. For 40 or 50 

 rods the shore is fringed by a ridge, about a rod wide and five or six feet high, of coarse 

 gravel and bowlders. The outer side is perpendicular, and the inside slopes gradually 

 towards the water, having the shape of a rampart in a fort. llev. S. R. Hall, who was 

 with us, stated that he had seen the same phenomena on other small lakes or ponds, and 



