igoo-i.] Physical Geology of Central Ontario. 153 



Laurentian, where they seem " almost always to be slightly accommo- 

 dated to the worn surface." Laflamme ('84, 15 ; '86, 43) has noted 

 similar features in the Lake St. John region ; and Adams ('93, 338) 

 has drawn attention to the fact that the rocJie moutonnce character of the 

 Laurentian rocks was impressed upon them in pre-Cambrian times.* 



Outliers. — Similar evidence as to the character of the pre- 

 sedimentary surface is offered in the vicinity of the numerous outliers 

 upon the crystallines. 



Conclusions. — In Central Ontario, from the evidence afforded by the 

 inliers of Archean within the area of Paljeozoics, and of the outliers of 

 Palaeozoic strata upon the Archean, it seems that the sediments were 

 laid down upon an uneven floor essentially the same as that presented 

 at the present day by the Laurentian areas along the borders of the 

 Cambro-Silurian escarpment. 



Examples elsewhere. — These buried oldland surfaces are found in 

 many other localities. Sometimes the eroded surface is almost a plane, 

 as seen in the Grand Canon section of the plain upon which the lower 

 Palaeozoic deposits rest. Again the surface may have had irregularities 

 many hundred feet in height, as shown by the Baraboo ridge in 

 Wisconsin, or as seen in an area in the Scottish Highlands, described 

 by Geikie. (See Newberry, '58, 57 ; Irving, '72, 99, and '77, 427 ; 

 Button, '82, 209; Geikie, '88, 400; Bell, '94, 362; Keyes, '95, 58; 

 Van Hise, '96, 59). 



Second Problem, Date of Erosion.— The second and third 

 problems for consideration have reference to the time and conditions of 

 erosion by which this pre-sedimentary topography was produced. 



From the writings of the earlier geologists the prevailing view seems 

 to have been, that the Palaeozoic sediments were laid down upon a 

 rising sea bottom, and that the Archean areas in Canada represent the 

 first emerged land. The more recent view is that the sediments were 

 accumulated on a sinking land surface. 



In this area, the granites, gneisses, and schists date from Archean 

 time. The evidences of a vast amount of denudation afforded by the 

 truncating surfaces, and the absence of lower and middle Cambrian 

 sediments from every portion of the area, make it improbable that 

 during the deposition of these sediments elsewhere the land here was 

 below sea level. The consensus of opinion, based upon the study of 



* See also Lawson, 1890. 



