470 A. A. .TFLIKX AMPHIBOLK SCHISTS OF MAXHATTAX ISLAND 



tion of the Manhattan schists, nearly 2 miles in length, indicated the 

 inclosure of a nearly continuous sheet of the hornblende gneiss from 

 river to river, brought up to view on one side of every anticlinal fold 

 and descending on the other. Combining this evidence with that from 

 the cross-section at Fifty-eighth to Fifty-ninth street, there is reason to 

 assume the existence of at least one interrupted sheet, here and there 

 split up into thinner layers, closely adjacent, or perhaps two horizon 

 planes in the Manhattan series, over which this basic material has been 

 spread or throughout which it has been injected. In other words, a 

 large number of these outcrops plotted on the map (plate 60) may after 

 all represent but one or two intrusions. 



INTERSECTION OF GNEISSES BY APOPHYSES 



The characteristic form of these basic sheets, that of intercalated len- 

 ticular layers, is met ever3Mvhere in strong contrast b}^ that of the later 

 intrusions of pegmatite, which cut across all the beds in dikes and veins. 

 Since the foliation of the gneisses is accepted as practicall}' coincident in 

 general with original bedding, it seems difficult to correlate their limited 

 shearing with such complete distortion of an apparently large number 

 of intersections by basic dikes — a distortion which at least has not ex- 

 tended to the later system of acid dikes. 



In discussing this point with Professor R. W. Brock, of Kingston, 

 Ontario, he has called my attention to the remarkable similarit}^ of con- 

 ditions in our Manhattan series to those of the same age in the West 

 Kootenay district of British Columbia. There a heavy formation of 

 schists occurs, the Shuswap series (assigned with probability'to Cambrian 

 time), which consists of mica schists, mica gneisses, crystalline lime- 

 stones, dolomites, and quartzites. Intercalated among them dark horn- 

 blende schists were found, and wdiite schists originally considered 

 quartzites but later identified as aplites. For a long period no crossing 

 of any beds of the series by either of these members was detected ; but 

 it was found later that the whole series had been cut bv a network of 

 diorite, granite, pegmatite, and aplite dikes ; so that " a large proportion 

 of the Shuswap and Cambrian schists represent igneous rocks which have 

 been crushed and altered into their present conditions," and that " the 

 oldest, as far as ascertained, consist of a series of basic dikes cutting the 

 Shuswap group, but now in man}^ instances so altered and foliated by 

 pressure and other causes that they have the appearance of constituent 

 beds.''* Too much reliance can not therefore be safel}" given to nega- 



*G. W. Dawson, Geol. Surv. Can., Ann. Rep., vol. vii, 1894, p. 32 A, and vol. x. 1897, summary, pp. 

 29-31 .\ ; see also side notes on Shuswap map sheet, Kamloops district. 



