36 NEW YORK STATE MUSEUM 



above the sea, an elevation sufficient to overtop the highest peak of 

 the present Laurentides ; for, according to Logan, '' in the country 

 between the Ottawa and Lake Huron the highest summits do not 

 appear to exceed 1500 or 1700 feet, though one . . , probably 

 attains 2300 feet ".^ We assume of course with good reason that 

 the Laurentides at that period were much higher than now, for they 

 must have suffered enormous erosion during the long interval since 

 the close of Siluric time.^ 



Since the deposition of these Siluric strata the region under con- 

 sideration has suffered an enormous amount of denudation, having 

 been brought to the condition of a low nearly level tract or pene- 

 plain, but little above sea level, not once, but probably a number 

 of times, separated by periods of elevation and at least one of sub- 



^Logan. Geol. Canada. 1863. p. 5. 



'The Niagara beds of Lake Temiscaming, in the great pre-Cambric area 

 of Canada and 150 miles distant from the nearest beds of the same age, 

 are of interest in this connection. They occupy an area about 300 miles 

 due north of Lewiston and on the north side of the present Laurentide 

 chain. According to Logan they do not properly belong to the forme'r 

 extension of the Niagara beds of the region under consideration, but rather 

 to the Hudson bay area on the north. They are of interest however as 

 showing the great former extent of these formations. They lie uncon- 

 formably on the pre-Cambric rocks, and the basal members are generally 

 sandstones and often conglomerates " containing large pebbles, fragments, 

 and frequently huge boulders of the subjacent rock" (Logan, p. 335). The 

 thickness of the formation here is estimated at between 300 and 500 feet. 

 The Ordovicic and Cambric strata are absent, showing a progressive 

 encroachment of the sea on the old-land, and a consequent overlapping 

 of the strata. Outliers of earlier strata are found in more southern por- 

 tions of Canada, resting on the pre-Cambric surface, and many of these 

 indicate a progressive overlapping of later over earlier beds. Lawson 

 holds that this indicates, that most of the Canadian old-land was covered 

 by the early Paleozoic strata, and that erosion since Paleozoic time has 

 resulted in simply removing these overlying rocks. (Bui. geol. soc. Arn. 

 I : 169 et seq.) He holds that comparatively little erosion of the old-land 

 has occurred since Paleozoic time, the present surface being essentially 

 pre-Cambric and only revealed by stripping of the overlying rocks. It is 

 not improbable however that some of these distant outliers may have been 

 preserved during the extensive denudation of the old-land, by having been 

 faulted down previously in a manner well known to have occurred in the 

 Scandinavian old-lands, a solution suggested to me by my friend, A. W. G. . 

 Wilson, of Harvard university. 



