GEOLOGICAL HISTORY OF THE LA URENTIAN BASIN. 403 



occur when a shore line gives place to other records. For example: 

 some of the ancient beach ridges about the west end of Lake 

 Erie have been found to be continuations of moraines. In other 

 instances shore ridges have been reported to end indefinitely and 

 to be replaced at the same general horizon by glacial records of 

 various character. The correct interpretation- of phenomena of 

 this nature is especially important. 



Accurate measurements of the vertical intervals between well 

 defined beaches at many localities would enable one to identify 

 special horizons, providing orographic movements were not in 

 progress during the time the series was forming. This method 

 has recently been successfully applied on the north shore of 

 Lake Superior, where the character of the country does not 

 admit of the tracing of individual terraces for considerable 

 distances. 



The deltas of tributary streams should also be revealed in the 

 topography of the basin of an ancient water body. Changes in 

 the character of lacustral sediments near where rivers emptied 

 are also to be looked for. Sand dunes are frequently an impor- 

 tant accompaniment of existing shores, and their association, 

 perhaps, in a modified form, with ancient beaches is to be 

 expected. 



5. Fossils. Thus far only a few fossils have been found in 

 the stratified clays and sands or in the ancient beaches of the 

 Laurentian basin. Such observations as have been made in this 

 connection indicate an absence of the remains of marine life and 

 the presence, in a few instances, of fresh -water shells in all of the 

 basin west of the eastern border of the basin of Lake Ontario. 

 To the eastward of Lake Ontario, however, in the St. Lawrence 

 and Champlain valleys, marine fossils are common in deposits 

 supposed to be contemporaneous with the stratified clays to the 

 west. 



A careful search in the clavs and beaches left by the former 

 water bodies might be rewarded by important discoveries. In 

 this examination microscopical organisms should not be neg- 

 lected. If after a detailed examination no fossils are dis- 



