SUMMARY. 189 



below the existing surface. Since, however, the gnuiites were exposed at 

 the surface, when the basal beds of the Marquette series were fornu^d (as 

 shown by the numerous bowlders of granite in tlie bjisiil conglomerjites), 

 it necessarily follows that the interval between the intrusion of the granites 

 and the formation of the first of the Marquette beds was of great length. 

 Since, moreover, the green schists are older than the granites, it further 

 follows that the schists are verv much older than tho oldest members of the 

 Marquette series. 



The greenstone - schists studied are all stjueezed surface materials. 

 They are nearly all reerystallized l)asic tuffs or altered lavas. The few 

 schists of doubtful origin were probably lava flows of coarser grain than 

 the predominant ones. As these rocks were surface forms, it is evi- 

 dent that there nuist have been a foundation upon which they were laid 

 down. The gnei>;soid granites can not have composed this foundation, 

 because they are younger than the schists. The former, ho\ve\er, are the 

 only other class of rocks, with the exception of the dikes, that liave been 

 discovered in those portions of the Northern domjilex studied; hence it 

 follows that the surface on which the basic lavas and tuff's were laid down 

 has not yet been found. It is barely possible that the original surface 

 rocks have disappeared, as Lawson' has suggested in explanation of a 

 similar set of phenomena in the Rainy Lake district of (Janada, and that 

 the granites and gneisses are their fused representatives; but in the ]\Iar- 

 quette district there is no evidence to show tliat this is the case, and we 

 must therefore content ourselves for the })resent with the statement that the 

 basement on which tlie schists were dei)Osited is unknown.- 



It is to be remarked in conclusion that, whatever may have l)een the 

 original condition of the granites, all the members of the Northern Complex 



' A. C. Lawson, Report ou the geology of the Rainy Lake regiou : .\nu. Rept. Geol. and Nat. Hist. 

 Siirv. of Canaila for 1887-88. Vol. Ill (new ser.), F., pp. 1-196; and Am. Jour. Soi., 3d series, Vol. XXXIII, 

 1887, pp. 473-480. Also Congres g(>ol. internat., Compte-rendn 4th sess., London, 1888, pp. 130-152. 



-Kominger's theory of the structure of the district under consideration is very similiir tci Law 

 son's theory, so far as it concerns the relations of the gr.anite8 to the other members of the Fundamental 

 Complex and to those of the Marquette series (see Chapter I, p. 84), and Rominger's statement was 

 published much earlier than Lawson's. The same remarks that apply to Lawson's suggestion apply 

 as well to Rominger's theory. 



