[amr] SYNOPSIS OF THE GEOLOGY OF CANADA 223 
Interior Continental Plain.—Overlying the greater portion of the 
pre-glacial surface of this region are found a sheet of superficial sands, 
clays, and gravels, filling in and levelling up many of the irregularities 
in the surface of the Ordovician, Silurian, Devonian, Cretaceous and 
Laramie rocks, whilst in the case of many of the rolling hills, they 
serve to add to the surface irregularities. The following section of 
Quaternary rocks in the prairie region is given from the reports by Dr. 
Dawson and Mr. Tyrrell :— 
Stratified sands, gravels, and silts. 
Upper boulder clay. 
Interglacial deposit with peat. 
Lower boulder clay. 
Quartzite, shingle, and associated beds. 
The boulder clay consists of sand and clay held firmly together, 
holding pebbles composed of quartzite and gneiss in the eastern portion, 
whilst the percentage of quartzite pebbles becomes reduced out on the 
plains and sandstone pebbles more numerous, with fragments of lignite 
usually present. Ancient drainage systems, anterior to the present one, 
have been detected in many portions of the North-west territories. In 
the Athabasca lake and Churchill river districts, according to Mr. Tyrrell, 
the quaternary deposits include:—(4) Recent lake beaches and flood 
plains of the present streams; (3) Sand plains; (2) Ancient shore lines ; 
(1) Till, drumlins, moraines, kames, eskars, and ispatinows. It is not 
at all unlikely that marine sediments constitute part of the prairie re- 
gion of Canada. Glacial Lake Agassiz has been described by Warren 
Upham from Manitoba and adjoining districts. 
The Albertan drift formation ‘“ belongs doubtless to the stage of 
general accumulation of the Ice Sheet followed by some recession, and © 
then by the maximum glaciation known as the Kansan stage.” 
The Cordilleran Region.—The Cordilleran glacier is defined by Dr. 
Dawson as the ice cap, during the early portion of the glacial period, in 
British Columbia, which attained a maximum development of nearly 
1200 miles in length from north to south. The main gathering ground 
of this ice sheet was between the 55th and 59th parallels of north 
latitude, extending in opposite directions, traversing to the Coast ranges, 
then filled the wide valley between Vancouver island and the mainland. 
The ice there divided and flowed in opposite directions, as subsidiary 
glaciers of Queen Charlotte Sound, and the Straits of Georgia. During 
the maximum of the Cordilleran glacier this region stood at a level con- 
siderably higher than it now does, and the great plains were probably 
depressed so as to admit waters from the sea. The retreat of the Cor- 
