TRANSACTIONS OF SECTION C. 635 



the district— in so far, at least, as litbological characters may be depended on. 

 They include a preponderance of thinly bedded limestones and dolomites, liner in 

 grain and usually less altered than those of the typical Grenville Series, associated 

 ■with conglomerates, breccias and slates still retaining complete evidence of their 

 clastic origin. 



It is in this Hastings region that careful investigation and mapping are now 

 in progress by several members of the Canadian Survey, with the prospect of 

 arriving at definite results respecting the relations of the Grenville Series and the 

 Huronian. It is too early to forecast what these results may be, for the question 

 is one which must be approached with an open mind ; but the work already com- 

 pleted by Messrs. Adams, Barlow, and Ells, appears to sustain the suggestion that 

 both series occur, and to indicate that they may there be so intimately connected 

 as to render their separation difficult. It must be borne in mind that, although 

 the relations of the Grenville Series and those of the recognised Huronian to the 

 Fundamental Gneiss are very similar, they characterise distinct tracts, to which 

 the Hastings district is to some extent geographically intermediate, although most 

 closely connected in this respect with the Grenville region. 



Reverting to the original classification of the Archaean of the Canadian Survey, 

 as developed in the field by Logan and his assistants, we may now enquire — In 

 how far does this agree with the results of later work above outlined ? In the 

 main, this classification still stands substantially unaltered, as the result of all 

 honest work carefully and skilfully executed must. The nomenclature adopted is 

 still applicable, although some of our conceptions in regard to the rocks included 

 under it have necessarily undergone more or less change. 



The Laurentian is still appropriately made to include both the Fundamental 

 Gneiss and the Grenville Series ; although at first both were supposed to represent 

 ' metamorphic ' rocks, it was even then admitted (1855) that these embraced some 

 plutonic masses practically inseparable from them. Later investigations have 

 increased the importance of such plutonic constituents, while at the same time 

 demonstrating the originally supposed sedimentary origin of the characteristic 

 elements of the Grenville Series ; but the admission of so large a plutonic factor 

 necessarily invalidates in great measure the estimates of thickness based upon the 

 older reasoning, under which any parallelism of structure was accepted as evidence 

 of original bedding. 



Whatever views may be held as to the propriety of including rocks of the two 

 classes under a single name, the necessity of so doing remains, because of the 

 practical impossibility of separating them over any considerable area for the pur- 

 pose of delineation on the map. I^o advance in knowledge is marked in substi- 

 tuting for Laurentian, with its original concept of a stratified time-series, such a^ 

 name as 'Basement Complex.' It may, indeed, yet prove that the homogeneity of 

 the Laurentian is greater than is at present supposed, for a mass of strata 

 that included ordinary sediments, arkoses, and contemporaneous volcanic deposits 

 of certain kinds, in which the arkose and volcanic constituents preponderated in 

 the lower beds, might, under metamorphism at great depths, produce just such a 

 combination as that of the Grenville Series and the Fundamental Gneiss, the latter 

 representing an aggregate result of the alteration of that part composed chiefly of 

 volcanic material or of arkose — in fact, under the conditions assumed, the lower 

 mass could not now well exist under any other form than that actually found in 

 the Fundamental Gneiss. In his address at the Nottingham Meeting of this- 

 Association, Teall has clearly pointed out that, in such cases, the chemical test 

 must necessarily fail, and that the character and association of the rocks them- 

 selves must be given a greater weight. 



The Huronian proper, under whatever local names it may be classed, still 

 remains a readily separable series of rocks, with peculiar characters, and econo- 

 mically important because of the occurrence in it of valuable minerals. 



The subsequently outlined Labradorian has been eliminated as a member of 

 the time-series, and the rocks of the so-called ' Hastings Group ' remain yet in a 

 doubtful position, but with the promise that they may afford a clue to the true 

 relations of the Grenville Series of the eastern and the Huronian of the western 

 province of the Protaxis. 



