KBLATIONS OF THE ^SASKATCHEWAN" GRAVEL 563 



tied the slopes and lower surfaces that had been reduced by degradation 

 prior to the early advance of the mountain glaciers. The gravel under- 

 lying the lower boulder-clay of the Keewatin ice-sheet at Lethbridge may 

 be preglacial. On the other hand, it may be that the pre-Wisconsin ex- 

 tension of the mountain ice preceded by a short interval the deposition of 

 the lower boulder-clay by the continental glacier in the same way that the 

 later mountain glaciers reached their greatest extension and began to 

 retreat before the last Keewatin ice-sheet reached its farthest limit. If 

 this was the case, then the gravels underlying the lower till at Lethbridge 

 may be correlated with this pre-Wisconsin stage of mountain glaciation. 

 Where quartzite gravel underlies the later mountain till, whether within 

 or beyond the limit of extension of the last drift of the Keewatin ice- 

 sheet, we are inclined to regard it as an interglacial deposit derived by 

 erosion from earlier drift on the higher levels. 



Application of the Name "Albertan" 



The relations of the several glacial and interglacial deposits in this 

 region being such as described above, question arises as to the application 

 of the name "Albertan" proposed by Dawson. 



Following the presentation of observed facts in the paper on the glacial 

 deposits of southwestern Alberta, 21 Dawson presented some theoretical 

 deductions, regarded as "the more obvious conclusions to be derived from 

 these facts and their interrelation." In the course of the present paper 

 reference has been made to some of the main conclusions which Dawson 

 presented and some quotations from this summary have been given. The 

 discussion of the conditions of deposition of the drift on the Porcupine 

 Hills have not been considered in detail, and this need not be done in the 

 present paper. Eef erring to the series of stages which Prof. T. C. Cham- 

 berlin had formulated 22 within the year immediately preceding the pub- 

 lication of the paper on the glacial deposits of southwestern Alberta, 

 Dawson suggested what he regarded as "the probable relations of the 

 glacial deposits of Alberta to this general classification." 



It is not necessary to consider in this place all the particulars of the 

 correlation proposed by Dawson. Tt should be stated, however, that he 

 suggested the correlation of the lower boulder-clay exposed on Belly River 

 with the "Kansan formation" of the Mississippi Valley. The name 

 Kansan was at that time applied to the fill-sheet underlying the Aitonian 



21 Bull. Geol. Soc. Am., vol. 7, pp. 81-58. 



22 T. C. Chamberlln : The classification of American glacial deposits, Journal of ecol- 

 ogy, vol. ill, 1895, pp. 270-277. 



James Gelkle : The Great Ice Arc, 8d od., chap, xll, 1894. 



