36 G. M. DAWSON — GLACIAL DEPOSITS OP SOUTHWESTERN ALBERTA. 



Ij'ing " quartzite shingle," subsequently named by Mr McConnell the 

 "Saskatchewan gravels,"'^ was, however, seen in a number of })laces 

 along the Bow, the evidence here, as elsewhere, being such as to show 

 that this deposit, although widespread, is generall}" characteristic of the 

 relatively lower tracts of tlie plains. 



It is thus not often possible to determine, where boulder-clay is met 

 with in isolated exposures, whether the lower or upper boulder-clay is 

 represented, but it is probable that the upper or newest boulder-clay is 

 that generally seen in all the more superficial excavations. 



" (^verlyiiii; the boulder-clay are widespread stratitied deposits, the distribution 

 of whii'h assists materially iu giving uniformity to the tracts of level plain. It is, 

 indeed, quite exceptional to find the surface soil consisting of boulder-clay disinte- 

 grated in place, and this (ururs only on the slopes of plateaus, or in hollows formed 

 by denudation. That the beds overlying the boulder-clay have not been merely 

 formed by its rearrangement in water without the addition of new material, is in- 

 dicated by the fact that in many places erratics nnich lar<jer than those character- 

 izing the boulder-clay of the locality are found strewn over the surface of the 

 country.! The beds observed in river sections and elsewhere to overlie the boulder- 

 clay are generally gravels or sands below and sandy or clayey loams above. The 

 latter form the subsoil over most of the region, and are generally rather pale 

 brownish- or yellowish-gray in color," 



Further study has served to verify and in some directions to amplify 

 the statements summarized in the foregoing paragraphs. 



On tlie subject of terraces and water-leveled tracts it is said in the 

 same report : 



"Terraces are prominent features in some parts of the river valleys in this dis- 

 trict, but are generally clearly due to the ai-tion of the river itself at a former 

 period. The extensive tracts of almost j)erfectly level prairie which occur, atlbrd 

 evidence of water action of some duration and may be regarded as wide terraces." 



The conditions of the drift deposits in the region of the Porcupine Hills 

 were not fully examined at this time and it is merely stated in the report 

 that — ■ 



" The eastern face of the Porcupine hills appears from a distance to be very dis- 

 tinctly terraced, but this aspect was found to be due to the outcrop of the nearly 

 horizontal sandstone beds." 



Further and more extended investigation in 189-1 shows that while the 

 existence of these sandstone outcroi)S has contributed to the form as- 

 sumed l)y the Porcupine hills, true water-formed terraces also exist and 

 are actually found to extend to very great elevations, as more fully noticed 

 in the sequel. 



Respecting the general aspect of the drift deposits in the foothill re- 



tOr "South SasUatcliewan gravels." Ann. Rep. Geol. Survey of Canada, vol. i, new series, p. 70 C. 

 X Compare McConnell. Op. cit., p. 74 C. 



