430 . Canadian Record of Science. 



These horizontal and unaltered beds of Cambrian (Pots- 

 dam and CaJciferons) and Silurian age, lie directly on the 

 tilted edges of the folded Lauren tian rocks of the chief 

 pro taxis as well as upon the accompanying anorthosites, 

 both of which had been deeply eroded before their depo- 

 sition. 



The intrusions of anorthosite are therefore undoubtedly 

 of pre- Cambrian age. 



Furthermore, although somewhat younger than the 

 Laurentian, which they cut, the eruptions must have 

 taken place before the pre- Cambrian dynamic movements, 

 by which the Laurentian was folded, had ceased, for the 

 anorthosites were in part at least crushed with the Lau- 

 rentian, and then, with them, eroded in pre-Cambrian 

 times. 



Their relation to the Huronian is not known, since they 

 have not yet been found in contact with it. But they are 

 probably not of Huronian age, since enormous eruptions 

 of volcanic rocks took place also during the Huronian 

 time, and these have quite a different character, being 

 cliorites. 



The anorthosite intrusions, therefore, took place toward 

 the close of, or soon after, the Laurentian period. 



A noteworthy fact in connection with these anortho- 

 sites is their distribution along the southerly and easterly 

 limits of the protaxis, bordering the great ocean basin in 

 which the Cambrian rocks were deposited later on. In 

 those ancient times the eruptive rocks apparently followed 

 the same law as now obtains in the distribution of vol- 

 canoes, namely, that they occur along the borders of the 

 continents as belts around great oceanic depressions. It 

 might be objected that this regular distribution is perhaps 

 more apparent than real, the protaxis having been more 

 thoroughly explored along its borders than elsewhere ; 

 but this objection is not valid. A few more small areas 



