EXCURSION B 6 



MUSKOKA LAKES 



G. G. S. Lindsay, Leader. 



The Muskoka lakes region is known as the " Highlands 

 of Ontario." It contains numerous clear-water lakes and 

 many popular summer resorts. 



the laurentian. 



The rock cuttings along the branch railway between 

 Gravenhurst and Muskoka wharf afford excellent sections 

 of the Taurentian, bringing out clearly the method by which 

 the characteristic banded gneiss has been produced. Here 

 and there masses of dark green-grey rock may be seen, 

 sometimes of considerable area. These patches of diorite 

 schist or of biotite schist are, no doubt, metamorphosed 

 basic rocks, such as gabbro, older than the granite which 

 penetrates them as dikes and floats off fragments from their 

 margins. At first the fragments are angular and sharp 

 edged, but at a greater distance from the parent mass they 

 become rolled out as schistose streaks, and along with this 

 goes lit par lit injection of granite magma, sometimes as 

 thin, light-colored sheets, at others as distinct granite dikes. 

 The result is a strikingly banded gneiss, grey if the original 

 basic material was in larger amount, and flesh-colored with 

 thin, greenish bands where the granite predominated. 



Still later dikes of granite and also of coarse pegmatite 

 have penetrated in all directions the gneisses just referred 

 to, and one may observe the beginnings of a second opera- 

 tion like the first, blocks being broken off, rolled out and 

 injected with granite parallel to the schistosity. Evidently 

 the Taurentian gneisses represent a long continued series 

 of granite intrusions, diluting and attenuating more and 

 more the basic materials which once made the crust through 

 which the eruptions took place. 



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