;i4 



TIIK K !•; ACK l\ CANADA. 



ScHK.MK Ol" CoilUKLAllnN ol TIIIO PlIICXOMKNA oi' rillC (il.AOIAI, 

 l*KllIOI) IN rilK (JidtDII.M'lllAN lilOiilo.N AND TIIK KkoION OK 

 rilK (iltKAT I'j.AINS (in AsCKNIHNd ()|{|)i;il). 



CofiliHi iini /{iijlnii, 



( 'oidilluniii /one at a liigh I'luvu- 

 tioii. I'l'i'iod of iiKist si'\i'i'(' j^laci- 

 ation and niaxiniuin <Ie\'flopnii'nt 

 of tlio great Conlilleiaii glaeief. 



( ifailual siilisidencc of tlie Cor- 

 tlilleran I'egion and deiiay of tlie 

 great glacier, witli deposition of 

 tlie l)oidder elay of tiie Interioi' 

 Platean and tlie ^'^lkon Dasin, of 

 tile lower lioiilder elay of the 

 littoral, and also at a later stage 

 (and with greater sulniiergenee) of 

 the inter-glacial .silty l)eds of the 

 same region. 



Re-elevation of the C'oi'dilleran 

 region to a level prohaMy as high 

 as or somewhat higher than the 

 present. Maximum of second 

 period of glaciation. 



Partial sulisidence of the (^)r- 

 dilleran region to a level about 

 2,500 feet lower than the present. 

 Long stage of stability, during 

 which the white silts were laid 

 down. (Jlaeiers of the second 

 period considerably reduced. Up- 

 per boulder clay of the coast 



I{('</ioii (if till (Irutl /'/((iiix. 



Correlative subsidence and sub- 

 mi'igcncc of tilt' great plains, 

 with possilile contemporaneous 

 intrca.sed elevation of the Lauren- 

 tian axis and niaximnm develop- 

 ment of ice upon it. Deposition 

 of the lower boulder clay of the 

 plains. 



Correlative elevation of the 

 westein part of tiie great plains, 

 which was probalily more or less 

 irregular, and led to the produc- 

 tion of extensive lakes, in which 

 inter-glacial deposits, including 

 peat, were formed. 



Correlative subsidence of the 

 plains, which (at least in the 

 western part of the region) ex- 

 ceeded the first subsidence and 

 extended submergence to the base 

 of the Rocky Mountains near the 

 forty-ninth parallel. Formation of 

 second boulder clay, and (at a 

 later stage) dispersion of large 

 erratics. 



('orrelative elevtation of the 

 plains, or at least of their western 

 portion, lesulting in a condition 

 of etjuilibrium as lietween the 

 plains and the Cordillera, their 

 nhitire levels becoming nearly as 

 at present. Probable formation 

 of the Missouri Coteau along a 



