1899] Barlow— Archaean Conglomerates. 207 



of thinly bedded limestones dolomites, &c., cut through by great 

 massive intrusions of gabbro, diorite and granite. Detailed and 

 critical examinations over the whole area have led to 

 the belief that in the Grenville Series we have a more highly 

 metamorphosed portion of the Hastings Series. This extreme 

 alteration in the case of the Grenville Series is accounted for by 

 the intimate presence of muchgreater volumes of the associated ir- 

 ruptives and their relatively much more acid character. In 

 many of the previous geological descriptions of this and neighbor- 

 ing Archaean districts, it has been customary to refer in a rather 

 positive manner to the existence of conglomerates as an evidence 

 of the clastic origin not only of the Hastings and Grenville 

 Series but also of the enclosing Laurentian gneisses. Localities 

 were cited and descriptions given of such coarse elastics, and the 

 often perfectly rounded character of the contained fragments was 

 referred to as a certain indication of the wearing action of 

 runnino- water. • 



The fallacy of arguing the sedimentary origin of the 

 whole scries because of the presence of such comparatively in- 

 significant inclusions of clastic material, has been clearly shown 

 by recent Archaean work and is now very generally conceded. 

 It is not however so widely known that many of the con- 

 glomerates so-called and described have no existence as such 

 but are in reality autoclastic* rocks or dynamic breccias which 

 have resulted in the main from the complex folding and stretch- 

 ing occasioned by the operation of the strong orogenic 

 forces prevailing so intensely in pre-Cambrian times Murray 

 in 1853 and Macfarlane in 1866 refer to the presence of these 

 coarse beds in the A.rchaean of Hastings County, while on page 

 31 of the Geology of Canada (1863) conglomerates are referred 



* The term " auti^clastic " originally proposed by H. L. .Smyth (see Geology of 

 Steep Rock Lake, Am. Jour. Sci. .XLii, p. 331) is very applicable used as its aulhor 

 defines to rocks " which have formed in place from massive rocks by crushing and 

 squeezing without intervening processes of disintegration or erosion, removal and 

 depositon." Van tlise (see Principles of North American Pre-Cambrian Geology, 

 i6th Ann. Rep. U. S. Geol. Surv. p. 679. 894-95) explains the use of the term, de- 

 scribes the method of formation of these rocks and the means oi distinguishing ihcm 

 from basal conglomerates. 



