COMPARATIVE STRUCTURES ^^^" 109 



is younger than the Meguma, for it holds detritus from it, especially in 

 the east. Earlier than tliis came the Taconic revolution, separating the 

 Ordovician from the Silurian. This was moderate in the maritime 

 jjrovinces, but is shown by unconformity at the top of the Ordovician 

 wherever observable. But it can not be this which effected the folding 

 of the Meguma, for neither Silurian nor Ordovician reflects the type 

 of folding which characterizes that series. It is true that between the 

 catastrophic epochs named unconformities were made iji Nova Scotia. 

 These can be seen or inferred in various places between the different series 

 of rocks lying north of the Meguma sediments; but they are not pro- 

 found, nor can they be traced over any considerable distance, and in no 

 case does either series affected by the unconformity resemble the Meguma 

 in lithological or structural characteristics. 



In all the maritime region of British North America a great uncon- 

 formity separates the Cambrian and pre-Cambrian wherever they are 

 found in contact. This is true in the eastern townships, in New Bruns- 

 wick, and in Newfoundland. The very general distribution of this un- 

 conformity and the great hiatus which it represents render it probable 

 that a similar break separates the Cambrian and pre-Cambrian in Nova 

 Scotia, and that it is marked in this instance by the total unlikeness in 

 appearance, and especially in orogeny, between the Ordovician and 

 Meguma, or, to go farther afield, between the latter and the Cambrian of 

 southern Cape Breton. Not only this, but the folding had been accom- 

 plished in the older series before the erosion interval, and this may place 

 other phenomena in the series as pre-Cambrian, such as the formation of 

 the bedded veins. 



THICKNESS 



The thickness also is too great when comparison is made with any 

 known Cambrian in the east. It is four times as great as any of the 

 Cambrian in eastern Canada or Newfoundland, even under the liberal 

 definition of the term followed by Canadian writers, and it is twice as 

 great as any known Cambrian section in the United States. In southern 

 New Brunswick, but a comparatively short distance away, the thickness 

 of the Cambrian is slight, although all three of its main subdivisions are 

 represented. It is unexpected, to say the least, to find in the midst of 

 fossiliferous sections nowhere more than 6,000 feet in thickness an enor- 

 mous area nearly 30,000 feet thick and almost absolutely barren, as far as 

 known at present. 



INTRUSIVE s 



Another line of evidence is offered by the intrusives. Except a re- 

 markably small number of basic dikes, no intrusives but granites and 



