THE LA URENTIAN PENEPLAIN 665 



secondary cover. Everywhere that the bed-rock surface is known, 

 whether covered or not, it presents a smooth, hard surface, free 

 from the products of decay in situ. But not only is this true of the 

 portion of the plain remote from the bordering Paleozoic sedi- 

 ments, but the work of Laflamme, Adams, Lawson, and others has 

 shown that it is true of the localities adjacent to and mider the 

 Paleozoic cover. ^ Around the southern border of the peneplain, 

 in the Lake St. John region, in the Moose River basin, and in a 

 few other localities, the actual contacts between the Paleozoic 

 sediments and the pre-sedimentary peneplain surface are known. 

 In these cases it will be recalled that the peneplain facet upon 

 which the sediments rest is probably that of an earlier cycle 

 than the main Canadian peneplain. Now, in every case where 

 these contacts have been met with and examined it is found: 



1. That the crystalline rock surface under the sediments in 

 situ is as little altered as in the ice-scoured surface perhaps 

 twenty feet away. 



2. In some few localities the pre-sedimentary crystalline sur- 

 face retains some traces of decay, such as pits and pockets, now 

 filled with small outliers of sediments, isolated more or less from 

 the larger masses. Such pitted surfaces occur near Kingston. 

 The best known case is that described by Bell as occurring on 

 Benjamin Island, Lake Huron. 



3. In only .one locality south of the main divide has an actual 

 arkose, which is presumably derived from the decay of near-by 

 granitic rocks, been reported in situ. This forms the lowest 

 member of the Ordovician series of the locality, and rests upon 

 the fresh surface of a gneiss. The basal members of the pre- 

 Cambrian rocks in northern Labrador are arkoses whose mate- 

 rials probably have not been transported very far. 



As regards the apparently significant absence of arkose 

 deposits (which might be regarded as old soils i7i sitii) from 

 beneath the Paleozoic sediments, it is to be noted that in almost 

 all cases where the actual contacts between the sediments and 

 the crystallines are known they occur at the summits or on the 

 flanks of the crystalline ridges or domes. So far as the author 



'For references and details see 41, pp. 146-53. 



