﻿Vol. 64.] LAUEENTIAN STSTEM IN EASTERN CANADA. 143 



the dip naturally varies somewhat from place to place, but the 

 average dip may be taken as 45°. This is a minimum estimate, 

 the average dip along the whole section being in all probability 

 somewhat higher. This gives a thickness to the Grenville Series 

 along this line of section of 94,406 feet. 



It is scarcely possible that the series attains so enormous a 

 thickness, but it must be noted that along the whole length of this 

 section a continuous alternation of beds of varying character is 

 presented, and therefore it is not a foliation but a true bedding that 

 is observed and measured. It is, furthermore, to be noted that 

 although this series may have been repeated by isoclinal folding, 

 there is no stratigraphical evidence that such is the case, and this 

 folding has nowhere brought up the basement upon which the 

 series was deposited — a fact which indicates again that the series, 

 even if so folded, is extremely thick. 



It may be safely stated that the Grenville Series presents by far 

 the thickest development of pre-Cambrian limestone in North 

 America, and that it presents at the same time one of the thickest 

 series of pre-Cambrian sediments on that continent. 



ISTot only has the Grenville Series a great thickness, but it has 

 a great superficial extent. It is exposed more or less continuously 

 over an area of 83,000 square miles in Eastern Canada and the State 

 of New York. In areal extent, therefore, it can be compared in 

 North America only with certain of the greatest developments of 

 the Palaeozoic limestones, as, for instance, the Knox Dolomites of the 

 Southern Appalachians. In all probability, its original areal dis- 

 tribution was considerably greater than above stated, although this 

 cannot be definitely determined on account of the great erosion to 

 which the Laurentian protaxis has been subjected. 



It may here be mentioned that the ' Hastings Series,' a desig- 

 nation given by Logan to certain rocks of the Madoc district, has 

 proved, as Logan conjectured might be the case, to have no inde- 

 pendent existence, but to be merely the less metamorphosed portion 

 of the Grenville Series seen in the southern part of the Bancroft 

 area. It is, however, practically certain that in this Madoc district 

 the comparatively - unaltered rocks, which were designated by 

 Logan as the Hastings Series, really consist of two unconformable 

 series ; and it is possible also that in the Grenville Series, as shown 

 upon the Bancroft sheet, there may be two formations separated 

 by an unconformity — as suggested by the occurrence of certain 

 conglomerates, the position of which is shown upon the map 

 (PI. XIII). If, however, there are proved to be two formations 

 within this area, these are identical in petrographical character, 

 and are so intimately infolded and so highly metamorphosed that 

 their respective distribution in the Bancroft area cannot now be 

 determined. 



Q. J. G. S. No. 254. 



