STRUCTURAL FEATURES OF THE PRE-CAMBRIAN 267 



same composition, which in its turn is overlain by biotite or horn- 

 blende schists, representing similar material in a still finer state of 

 subdivision. The succession indicates a similar history in each case. 

 (4) The relations of each body of sediments to the underlying lava 

 series appears to be one of erosional unconformity; if structural un- 

 conformity also exists, the discordance is slight. Thus the period 

 elapsing between the outpouring of the lavas and the deposition of 

 the sediments was characterized in each case by gentle epeirogenic 

 movements only, not by intense orogenic movement. (5) The 

 close parallelism of the axes of the major folds of the different 

 areas indicates that all were deformed either by the same force 

 or by successive forces directed along the same lines; while a 

 study of the effects of shear on the different folds shows that each 

 body of sediment was deformed to about the same extent. These 

 two lines of evidence indicate that all the sediments were folded 

 at the same time, and by stresses of much the same strength. 

 (6) All the sediments have been intruded by granites, which, 

 though not proven to be of the same age, have not as yet been 

 shown to be of different ages. 



While, as previously stated, an entirely reliable correlation in 

 these pre-Cambrian rocks cannot be made in the absence of a 

 continuous sedimentary datum plane, nevertheless the foregoing 

 evidence indicates such a uniformity in the history of these scat- 

 tered patches of sediments that it appears highly probable that 

 they are remnants of a single, once widely distributed formation 

 or series. So far as now known, this series may have been depos- 

 ited under marine conditions and have formed a continuous sheet, 

 or under continental conditions in separate settling basins. As 

 the time has not yet arrived for the correlation of these sediments 

 with other ancient sediments to the south and southwest, such 

 as the Timiskaming, Sudbury, and Hastings series, the writer 

 would apply a single local name to all those under discussion, 

 simplifying the nomenclature by the elision of the various local 

 names already appHed. The name Pontiac series, applied by 

 M. E. Wilson in 1909 to the sediments of the first discovered belt 

 to the south, has precedence; but in view of the doubt as to the 

 composition of Wilson's Pontiac series, as outlined on page 200, 



