54 G. M. DAWSON — GLACIAL DEPOSITS OF SOUTHWESTERN ALBERTA. 



Feet 



3. Boulder-clay, with some stratified silty layers and pebbles arranged in lines 



of stratification 20 



4. Gravels 15 



5. Laramie sandstones and shales, nearly horizontal 25 



100 





D 



Q.: 



The following details, written down at the time, further explain what 

 is seen in this interesting section. The order fol- 

 lowed is that of deposition, beginning with the base 

 of the section: The surface of the Laramie rocks 

 wliere composed of fairly hard sandstones is 

 smooth and waterworn without any glacial striae. 

 Resting directly upon this are rather incoherent 

 gravels with a considerable admixture of clayey 

 or silty matter. All the stones are derived from 

 the mountains, and most of them are quartzites 

 (some 18 inches through), l)ut Rocky Mountain 

 limestone is also abundant. Nearly all are well 

 rolled and rounded, but careful search shows traces 

 of striation on some of the limestone pebbles. 

 These appear to have been produced upon the 

 already rounded stones and to have been largely 

 obliterated afterwards by further wear. There is 

 little or no trace of stratification in the gravels, 

 which resemble more the deposit found in the bars 

 or 1)ed of some river than anything else. 



The gravels are cut off above sharply on a nearly 

 level plane, above which is a hard yellowish gray 

 boulder-clay, often standing vertical in the face 

 and l)reaking out in prismatic fragments. This con- 

 tains many well striated stones and small bould- 

 ers, and shows occasional lines, running for a few 

 feet or yards horizontally of fine pebbles and sand, 

 or of silt, wliich is slightly lighter in color than the 

 rest. The vast majority of the stones are from the 

 mountains, but a very few Laurentian stones are included. There is no 

 marked difference between the earthy material of the gravels and that of 

 the mass of the boulder-clay, except that the latter is more compacted, 

 and the gravels might in fact well be regarded as a species of boulder-clay 

 or a closely allied deposit. The l)oulder-clay probably varies from 10 to 

 20 feet in thickness within a few hundred feet. 

 The upper part of the boulder-clay becomes more interstratified with 



II i 



Figure a,.— Section in Bank 

 of Bow River near Calgary. 



A = Laramie rocks. 



B = Saskatchewan gravels. 



C = boulder-clay with silty 

 layers. 



Z> = stratified silts contain- 

 ing (A) a layer of 

 boulder-cla^-. 



E = surface gravels and 

 soil. 



