THE ILLINOIAN ICE INVASION 327 



point in the valley twice readvanced over it. " At this point a section exhibits 

 the following strata: 



Drumlin peak, X. 



Beach sands, 12-15 feet. First interval of recession. 



Fine layer of till, 4-5 feet. First readvance of ice. 



Sands of high terrace type, 22 feet. Second interval of recession. 



Till, 8 feet. Second readvance of ice. 



Coarse, cross-bedded sands, x. Third recession of ice. 



f 

 This section is 40 feet thick and the strata may be seen for upwards of hal 



a mile from north to south. Comparing this data with the paper of Clapp 18 

 it would seem to fit in with the general classification of glacial tills and inter- 

 glacial intervals. No biotic remains have been observed in the sands between 

 the tills. 



Somewhat recently, excavations in the City of Boston have uncovered strata 

 apparently referable to one or possibly two drift sheets of pre- Wisconsin age. 185a 

 The evidence for these "consists of a zone of extremely weathered material 

 beneath the Wisconsin drift, an erosion unconformity, different types of de- 

 posits, a slight trace of an interglacial soil, some interglacial subsoils, and an 

 apparent difference in the direction of the source of included debris. It was 

 possible to determine with some accuracy the zone of post- Wisconsin oxidation, 

 and the final shaping of the ridge in which this evidence was found appears to be 

 due to the readvance of an ice sheet which slightly contorted the upper- 

 most water lain materials. The axis of this ridge is accordant with the direction 

 of the striae of the last glacial advance in the region. " 



As is the case in New York State, evidence is accumulating which indicates 

 complexity in the glacial deposits of the New England States; and it will pro- 

 bably be found that several of the ice sheets overran this territory and were 

 separated by interglacial intervals correlative with those of the areas farther 

 west. 



10. CANADA 



a. The Toronto Formation 



The most complete interglacial biota at present known is contained in the 

 sands and clays at Toronto, Ontario. These are placed by Coleman 185 in the 



I8ia Wentworth, Science, N. S., XLII, p. 58. 



'"Interglacial Periods in Canada, pp. 12-14. Coleman later (Bull. Geol. Soc. Amer., 

 XXVI, pp. 243-254) refers these fossil remains to the Aftonian interval. The fauna is, how- 

 ever, more like that of the Yarmouth or Sangamon. The complexity of the upper drift de- 

 posits seems referable to the fluctuations of the ice fronts of later ice sheets. The Aftonian 

 contains a number of extinct mammals which are absent from the Toronto formation, and the 

 position of the Toronto deposits with relation to the old soils and other interglacial phenomena 

 of adjacent regions, seems to place it rather in the Sangamon Interglacial interval. 



