STRUCTURAL FEATURES OF THE PRE-CAM BRIAN 265 



limestone members in every case is also significant of the preva- 

 lence of similar conditions of deposition over the whole region. 



Structural similarities fonn perhaps the best evidence for the 

 correlation of these patches of sediment. Each area is a remnant 

 of a close fold, and the amount of deformation during folding 

 was approximately the same in all. On the flanks of the folds 

 the whole body of rock has been converted into schist, even the 

 competent basal conglomerate. The pebbles of the conglomerate 

 in each case have been flattened and sheared, the softer stretched 

 to mere strings, while the hard granites have suffered very little. 

 The axes of the folds show remarkable similarity in strike. The 

 general strike of the Pontiac area is east-west; of the Mattagami 

 area, N. 80° E.; the axis of the Kenoniska and Lucky Strike 

 folds strike S. 75° E.; of the Brock fold, N. 85° E. These varia- 

 tions in strike are very small, considering how widely the districts 

 are separated from one another, and the conclusion therefore 

 seems justifiable that all of these sediments preceded, and were 

 deformed by, one period of regional stress. As the region has 

 been gently cross-folded, the variations in strike most probably 

 are due to this, though perhaps also in part to disturbance by the 

 later intrusion of the granite batholiths. 



The different patches of sediments are similar in their rela- 

 tions to the older lava series. In almost every case it has been 

 shown that the sediments rest unconformably on the lava series, 

 since the basal conglomerate contains rounded pebbles of all the 

 underlying rocks. As to the nature of the unconformity, a close 

 paralleHsm of strike and dip obtains between the two series, 

 indicating either that they were folded at one time or that a pos- 

 sible earher gentle folding of the lavas was obscured by more intense 

 shear after the sediments were laid. down. In the case of the 

 Kenoniska and Lucky Strike areas, the basal conglomerate was 

 observed to rest on different types of rock from point to point, 

 but whether this was due to differential erosion of the under- 

 lying rocks previous to the deposition of the conglomerate or to 

 original irregularities of deposition in the underlying series was 

 not determined with certainty. It is believed, however, to have 

 been due to erosion, since in the case of the Lucky Strike area 



