28 THE ROYAL SOCIETY OF CANADA 



though the width of the zone of intermittent submergence must 

 have been at times very great and shore deposits or near-shore deposits 

 were projected far out with every important period of uplift which 

 affected the depth of the sea. Attempts at correlation by means 

 of the fossil remains have been successful to a certain extent ; but the 

 change in fauna and flora during the latter part of Cretaceous 

 time was not very marked, so that much of this evidence in fixing 

 the age of the various beds lacks the defîniteness that is desirable. 

 This is particularly noticeable in the brackish-water fauna of the shore 

 deposits of the edge of the Pierre sea as found in the Belly River and 

 Edmonton formations. 



The fluctuations of the sea margin are taken to be an expression 

 or reflection of the earth movements in the comparatively new land 

 areas to the west and, therefore, not liable to be local in character. 

 As the shallow water periods are well marked in the Cretaceous 

 deposits of Alberta a scheme of correlation based mainly on the Palseo- 

 geography of the region is submitted. An exact synchronism is not 

 claimed for all the shallow-water deposits here grouped together ; but 

 it is claimed that the shallow-water periods are the elïects of earth 

 movements which must have been of considerable magnitude and, 

 therefore, they are of more value as time markers than the evidences 

 of subsidences which follow, because the latter are due in a great 

 measure to the shifting of load, the accomplishment of which may have 

 occupied various intervals of time. 



The marine Cretaceous deposits in the central part of the con- 

 tinent have been divided into two groups, the earlier called the Colo- 

 rado and the later the Montana. Both groups are made up mainly 

 of dark shales, showing that the sea was muddy and probably shallow. 

 The deposits denoting deeper water, which occur frequently in the 

 central areas, contain occasional calcareous beds, but in general the 

 sea-water was plentifully supplied with arenaceous material. 



THE COLORADO GROUP. 



This series resting on the fresh-water deposits of the earlier 

 Dakota formation is divided into two main divisions, the lower, the 

 Benton shales, which are found very widely distributed, thus marking 

 possibly the greatest extent of the Cretaceous sea (Plate I), and the 

 upper, the Benton-Niobrara (Plate III). In the upper division 

 the name Niobrara has been applied to a series of clear-water calcareous 

 beds. These are recognized in the eastern division in Manitoba. 

 In the sections in the middle portion of the plains there is no distinct 

 divisional line, clear-water portions occurring all through the middle 



