FORMER ERRORS IN IDENTIFICATION. 488 



larly along the margins of the outcrops. In the same way also great 

 areas of greenstone or dioritic rocks found in the Huronian system at 

 various places have at some time assumed the character of chloritic 

 schists. 



The periods of folding and crumpling by which these changes of struc- 

 ture were produced varied in different localities. Thus, in the Lauren- 

 tian area the plications resulted from agencies which acted prior to the 

 deposition of the Potsdam sandstone, since this formation flanks the 

 Laurentian rocks in a horizontal position and even occurs in a few scat- 

 tered outcrops at points in the area itself. It is probable also that many 

 of the present mineral-bearing veins or dikes were developed at this time, 

 while in the case of the dioritic and syenitic rocks of the Eastern Town- 

 ships this folding, schistosity and overturning were subsequent to the 

 Upper Silurian time, since fossiliferous strata of that age were involved 

 in the crumpling to such an extent as not only to impart a truly schistose 

 structure to the fossiliferous slates themselves, but in places to overturn 

 them so comijletely as to place them directly beneath the slates of the 

 Cambro-Silurian system. 



Thus it will.be seen that the hyj^othesis which assumed that the greater 

 portion of these intrusive gneissic and foliated portions of the system, 

 though in places this foliation is lacking, was an integral portion of the 

 sedimentary series, was a natural one, more especially when we find that 

 many of the smaller dikes or bands of p3a'oxene, anorthosite and felspar 

 have been intruded along the bedding-planes of the gneiss; and hence 

 we find the deposits of mica, apatite, etcetera, frequently described as 

 bedded developments of these minerals, on the ground that the pyroxene 

 rock was also sedimentary, while tlie occurrence of apatite-bearing bands 

 in certain i)laces, in unconformable rehition to the sedimentary gneiss, 

 led to the supposition tliat certain of these deposits were vein-masses 

 rather than l)eds. 



MlNKI^\LS. 



Rock Reldtioiis determined by Mlaemh. — The many openings which have 

 been made in the apatite and mica deposits of the Gatineau and Lievre 

 districts, for these minerals juust to a certain extent be studied together, 

 have facilitated tlie elucidation of tliis problem very considerably, and 

 the relations of the associated or containing rocks can now be made out 

 with far greatdf exactness than in the days 'before the great value of their 

 mineral contents was discovered. Thus we find that while the strike of 

 the gneiss and limestones, extending over many thousands of square miles, 

 is very uniformly north to north 15° east, unless this has been deflected by 



