Petrographical Relations of Laurentian Limestones. 3 



a detailed geological examination of the area comprising 

 sheet 118 has been begun and completed by Dr. Adams 

 and Dr. A. E. Barlow. 



The geology of that particular portion whose limits 

 were given at the outset, and to which alone the following 

 remarks refer, may be described as follows : The country 

 is a hilly one, presenting the remarkable undulating or 

 roche moutonn6e surface so characteristic of the Laurentian ; 

 the depressions are usually filled with drift, and in the 

 flats so formed are found innumerable lakes. Countless 

 rounded bosses of bare rock protrude through the drift 

 especially in those portions of the area occupied by 

 several batholitic masses of granite or granitic gneiss, 

 identical in appearance with the Fundamental Gneiss, 

 which have penetrated and eaten into the white crystal- 

 line limestones which underlie the remaining portions of 

 the area. 



Dr. Adams has found in his recent studies in this area, 

 the results of which will be published shortly, that in 

 many localities at least, the Laurentian limestones, which 

 are always much altered, were, at the contact of the 

 Fundamental Gneiss, transformed into dark, basic rocks 

 which still retained the banded structure of the limestone. 

 He also ascertained that the Fundamental Gneiss con- 

 tained many inclusions of dark, basic rocks, which near 

 the contact were more angular in form, and away from 

 the contact often assumed the form of dark elongated 

 streaks in the Fundamental Gneiss. The field relations 

 were such that it seemed practically certain that these 

 fragments were portions of the basic contact rock, in a 

 still more highly altered condition, which had floated 

 away in the igneous mass during the process of intrusion. 



It would appear then, either that new igneous material 

 had been erupted through this limestone series, or that 

 the underlying Fundamental Gneiss had been reheated 

 sufficiently to fuse or to become plastic, and that the 





