THE KEEWATIN SKRIKS. ."> I.'I 



schistose phases of the altered traps. At the top of the series are found 

 soft, fissile, light-gray schists, micaceous schists and some altered clay 

 slates. Between the rocks which may he always recognized as the hasal 

 rocks ami those which appear to be always in the highest position in the 

 scale are a complex group of volcanic detritals, agglomerates, tuffs and 

 trap, ashes, felsite schists, sericite schists and fine-grained evenly schistose 

 quartz porphyries. Some of these rocks were probably thrown out as 

 volcanic ejectamenta and, falling in the waters of ancient lakes, were sifted 

 and stratified by their restless motion. In this way perhaps some of the 

 conglomerates have been formed. < )thers again are probably but volcanic 

 breccias, of which the harder fragments have been more or less rounded 

 in their passage through the vents and in subsequent movements before 

 they became consolidated in the matrix. On the Seine river the chlorite 

 schists in one locality contain abundant lenticules of quartz which are 

 often ver} r wide in proportion to their length, giving the rock a con- 

 glomeratic aspect. These again are sometimes lengthened out and appear 

 as irregular lenticular quartz stringers. While some of the Keewatin 

 conglomerates have the appearance of being true sedimentary depositions 

 on old beaches, there is yet a degree of uncertainty as to their character 

 and origin. These are lor the most part local in extent and narrow in 

 development and occur at various horizons in tin; middle and lower por- 

 tions of the Keewatin. They may, as Sir Archibald Geikie* says, " un- 

 doubtedly indicate Local disturbance connected perhaps with terrestrial 

 readjustments consequent upon the waning of volcanic energy;" but it 

 is extremely doubtful if in this part of the country they mark a great or 

 continuous break dividing the Keewatin rocks into a lower and upper 

 division at any recognizable horizon. Their significance seems to be 

 merely local. Professor Van Bisef attaches importance to several de- 

 scribed occurrences of conglomerates. In only one case, however, was an 

 undoubted unconformity observed below the conglomerate, and this may 

 be accounted for by the assumption of a fault. The collective extent of 

 all the conglomerates described by these authors is insignificant in com- 

 parison with the area, to which they would apply their conclusions. The 

 absence of unconformity of structure between the conglomerates and 

 underlying rocks, which is likewise, so far as observed, in the Canadian 

 area northwest of Lake Superior an invariable rule, is in itself a signifi- 

 cant fact, for the same cleavage-producing forces which might entirely 

 obliterate all original structure in the fine-grained schists would not 



♦Anniversary address before the Geological Society of London on "The volcanic Hoiks of Eng- 

 land." 1891. 



t " An Attempt to harmoniz : some apparently conflicting Views of Lake Superior Stratigraphy,'' 

 Am. Jour. Sci., vol. Ixi, p. 117, and "Observations on the structural Relations of the Upper Ilnro- 



nian, Lower Huron ian and Base at Complex on the north Shore of Lake Union," Am. .lour. Sci., 



vol. lx iii, p. 224. This latter paper was prepared in collaboration with Mr Pumpelly. 



