630 FRANK D. ADAMS 



deducted in arriving at the measurement just given, the Hastings road 

 passes continuously across the Hmestone and amphibolites of the 

 Grenville series, and throughout this whole distance crosses these 

 latter practically at right angles to their strike. 



Furthermore, throughout the whole distance these strata dip in 

 a southerly direction at high angles. Here and there, at long inter- 

 vals and for a few yards, a reversed or northerly dip can be observed, 

 but this is merely local owing to a minor undulation in the strata 

 which has no stratigraphical significance. 



The angle of dip naturally varies somewhat from place to place, 

 but the average dip may be taken as 45°. This is a minimum esti- 

 mate, the average dip along the whole section being in all proba- 

 bility somewhat higher. Taking this value we obtain the following 

 result : 



Apparent thickness of the Grenville series along the line of section 



= 25.3 miles= 133,584 feet. 



True thickness of the Grenville series along this line of section 



= 17.88 miles= 94,406 feet. 



It must be noted that the series is one which along the whole 

 length of this section presents a continuous alternation of beds of vary- 

 ing character, so that it is not a foliation but a true bedding that is 

 observed and measured. 



It is, moreover, to be noted that while this thickness is so great as 

 to suggest reduplication of some sort by isoclinal folding or by faulting, 

 there is no stratigraphical evidence that such reduplication exists, 

 and a fact of very great importance to be noted is that if there be such 

 reduplication, the basement upon which the series was deposited is 

 nowhere brought up along the whole hne of section as would undoubt- 

 edly be the case unless the series reduplicated by folding was of enor- 

 mous thickness. 



For purposes of comparison the estimated thicknesses of some 

 of the other great developments of pre-Cambrian rocks in North 

 America are presented on a later page. 



In all these districts there is, as in that at present under considera- 

 tion, a possible error due to partial repetition by folding. 



In the Grenville series, as has been stated, limestones predominate, 



