116 THE CANADIAN NATURALIST. [Vol. viH. 



These considerations relate chiefly to the depth of the sea in 

 which the more highly fossiliferous part of the Leda clay was 

 deposited, but other considerations indicate that the higher parts 

 of the Leda clay were formed in shallower waters. I have men- 

 tioned on a preceding page that the dark colored clays abound- 

 ing with organic matter, and containing shells which indicate the 

 depth of water above named, are overlaid at St. John by reddish 

 clay with sandy layers. Just above the " Falls" of the St. John 

 River in Fairville these upper clays may be seen to rest upon 

 eroded beds of dark clay, and at other points they rest directly 

 upon the tough red clays. This group of beds, which contains 

 fossil shells of the Laminarian zone, appears to have been laid 

 down when the land had risen to within one hundred feet of its 

 present level, and may be denominated the Upper Leda clay. 

 It, together with all the older portionjof the clay deposit, suffered 

 denudation preparatory to the deposition of the Saxicava sand, a 

 group consisting of grey, buff and brown sand, occasionally 

 capped or underlaid by gravel beds ; and which from the occur- 

 rence in it of littoral species only may be regarded as a tidal 

 deposit. 



[To bring all the known facts relative to the Post-Pliocene de- 

 posits in this region into harmony, it appears necessary to assume 

 that at the beginning of this age, Acadia and the neighboring 

 portions of the American continent were elevated to a height of 

 several thousand feet above the sea, and that the extensive plateau 

 thus formed was bordered on the south by deep oceanic waters. 

 Such a change in the relations of sea and land (accompanied per- 

 haps by similar movements under other meridians in the Northern 

 Hemisphere) would lead to the formation of a glacier zone 

 across New England and Canada, facing a sea open to the influx 

 of heated waters from the equatorial regions. As glaciers 

 formed in this way would receive accessions to their mass on the 

 southern side only, they would bear with immense weight upon 

 the coast line, and (supposing that the earth's crust possesses a 

 certain amount of plasticity) would have a tendency to depress 

 it beneath the sea, causing at the same time a corresponding 

 elevation of the interior region. As the coast-line sank from 

 this cause, the glacier-zone would gradually travel northward, 

 seeking the rising land, and in the deep waters in front of its 

 southern margin, mud and stones swept off the land by the 

 moving ice, would be deposited. Such a deposit would resemble 



