1869. J MACFARLANE — GEOLOGY OP LAKE SUPERIOR. 39 



shales just mentioned, there is found a conglomci-ate bed from 

 two to six feet thick (marked on the map yellow, with brown 

 spots). The pebbles are generally quartzite, red coloured and 

 jasper-like, and the matrix consists of coarse-grained red coloured 

 sand. Ked and white sandstones, coloured yellow on the map, 

 succeed the conglomerate. The white sandstones make up the 

 greater part of this group, but in many parts of its thickness, and 

 especially in the part immediately overlying the conglomerate, 

 layers of red sandstone are interstratified with the white beds, 

 and the latter frequently shew spots and irregular patches of red. 

 Sometimes, similar spots of white are observed in the red sand- 

 stone layers. The colouring matter of the red sandstone is 

 peroxide of iron, and the difference in composition between it and 

 the white is shewn in the following analysis. I. is the composition 

 of a red-coloured, and II that of a white portion of a specimen, 

 from a ridge of sandstone lying between Camp and Fork Bays: — 



I. IL 



Silica, insoluble in Hydrochloric Acid 73 '45 72 So 



Peroxide of Iron, with a little Alumina 2-41 o.gi 



Carbonate of Lime . 



13 '04 



Carbonate of Magnesia 10-94 ii'94 



99'34 98-78 



It will be observed that the cementing material of these sand- 

 stones has almost exactly the composition of dolomite. Sandstones 

 of this composition are probably not unfrequeut among the 

 Potsdam and Calciferous rocks of Canada, but, in Europe, they 

 are described as belonging exclusively to the Buntsaudstein 

 formation (Zirkel, Petrographie, ii., 581). In the upper part of 

 the group, red shales are found in great quantity, interstratified 

 with the sandstone, and apparently approaching in composition to 

 the indurated marl hereafter to be described. This group of '' red 

 and white dolomitic sandstones and shales" has a general dip of 

 7° to 15° eastward. The sandstones very frequently shew ripple 

 marks on the surfaces of the beds. 



A bed of limestone, from two to six feet thick, coloured blue 

 on the map, overlies conformably the group first described. In 

 the upper part, it appears brecciated from intermixed cherty 

 fragments, but in the lower part it is more crystalline. 



Immediately overlying the limestone, and beautifully exposed 

 on the shore eastward from Red Bay, there comes a considerable 

 development of the indurated marl mentioned by Sir W. E. Loo-an 



