ABSTRACTS AND DISCUSSIONS OF PAPERS 113 



Let us go much farther back in time. A similar stratigraphic banding exists 

 in argillites associated with the Huronian tillites at Cobalt, Ontario. I was 

 fortunate in being able to examine this section under the guidance of Messrs. 

 Miller, Knight, and Coleman during the International Geological Excursion in 

 1913, although they are not responsible for the following statement of obser- 

 vations. 



The banding has, I believe, been noted for a long time by the Ontario geol- 

 ogists and may have been discussed in their reports. At the south end of 

 Cobalt Lake occurs a thick bed of argillite delicately banded, indicating 

 rhythmic deposition. The bands are grouped in series which show larger 

 rhythms. If tbe bands are animal, the rhythmically recurring groups show 

 climatic fluctuations covering periods of years. On the southeast side of 

 Cobalt Lake the argillites are succeeded by a ripple-marked quartzite. The 

 thick till sheet rests on this without obliterating the ripples or crumpling the 

 argillite beds at a greater depth. The boulder conglomerate is faintly bedded 

 with grits and some beds of banded argillite show occasional subangular 

 boulders dropped into them. Many of the boulders are markedly soled and 

 indicate undoubted glacial wear. The whole suggests the presence of quiet 

 water, which at first was far enough from the glacier front to receive only 

 silt and clay. Later it was mantled apparently by an iceberg deposit rather 

 than a true ground till. This implies, however, true till in some region not 

 far distant. At a later stage there may have been an overriding of ice in this 

 same region. In other places at Cobalt what appears to be undoubted tillite 

 containing striated boulders rests directly on the floor of Keewatin rocks, 

 although the final proof, consisting of striatums 'on that floor, has not yet been 

 found. The association of these banded argillites with iceberg deposits and 

 ground moraine indicates, therefore, the existence of summer melting and 

 winter freezing during the Huronian glaciation. 



Sederholm also has found in Finland as far back as during Bottnian time a 

 regular alternation of clayey and sandy material which he interprets as an 

 annual stratification, explainable only by assuming a regular change of 

 seasons. 



Glacial conditions then seem to be brought about by a marked lowering of 

 the mean annual temperature of the whole globe, accompanied by an accentu- 

 ation of seasons in middle latitudes. This suggests a less effective spreading 

 out of equatorial warmth at such times and a more direct and rapid absorption 

 and also radiation of solar energy in the temperate zones. Glacial periods are 

 marked by strong seasonal climates, the emergence of winter. This is a fact 

 which, according to its distinctness, must enter into the adjustment of factors 

 bearing on the causes of Glacial periods. The explanation of non-glacial cli- 

 mates must, on the other hand, account for the submergence of winter in 

 middle and high latitudes with the earth's axis permanently situated as it is 

 at present. The explanation of glacial periods and of warm-pole periods are 

 equally important and complementary problems. The presence of marked 

 seasonal climates in temperate latitudes during glacial periods is an important 

 fact which must enter into that explanation. 



Mr. Frank B. Taylor : Laminated pebbleless clays formed in the preglacial 

 lakes which followed the retreating "Wisconsin ice-sheet occur in many places 

 in the Great Lakes region. A deposit of this kind occurs at Bracebridge, in 



