Professor A. P. Coleman — Changes of Level. 59 



II. — The Eelation of Changes of Level to Intekglacial Periods. 

 By Professor A. P. Coleman, Toronto University, Canada. 



THE interesting paper on "The Connection of the Glacial Period 

 with Oscillation of the Land," by Dr. Holst,^ while reinforcing 

 the quite probable theory that areas loaded with glacial ice sink 

 under the burden, and after the ice has been thawed rise again, 

 goes out of its way to deny the existence of Interglacial periods, 

 probably with the idea that there was only one important sinking 

 and rising in the Pleistocene, and hence no opportunity for Inter- 

 glacial times. However that may be in Sweden, the evidence in 

 favour of at least one important Interglacial period in North America 

 is too strong to be set aside for any mere theory. 



At the Meeting of the British Association in Toronto in 1897, 

 a number of British geologists had an opportunity of seeing sections 

 of the drift in the Don valley and at Scarboro' Heights near Toronto, 

 which show a very extensive series of sediments, rich in fossils, 

 lying between two well-defined sheets of Boulder-clay. 



A committee was appointed to work out in detail the relationships 

 of these Interglacial beds, and the secretary of the committee, the 

 present writer, aided by generous grants from the Association, 

 carried on a series of explorations the results of which were reported 

 at the three following meetings. A detailed summing up of the 

 facts observed, giving sections and lists of about 180 species of plants 

 and animals, chiefly forest trees, fresh-water shellfish, and beetles, 

 but including elephants, bison, and caribou, was published last 

 Summer in the Journal of Geology.'^ 



In a few words the general character of the facts observed may be 

 given here, so that the strength of the evidence may be appreciated ; 

 and lest there should be any doubt as to the reality of the Interglacial 

 position of the beds in question, it may be stated that they have been 

 visited by numbers of glacialists from the United States as well 

 as the Old World, some of them strongly opposed to the idea of 

 Interglacial periods ; but all have admitted that they are really 

 Interglacial, though there have been differences of opinion as to 

 whether the ice-sheet completely vanished during the time of their 

 deposition, or merely withdrew to a greater or less distance and then 

 advanced again. 



The Interglacial beds consist mainly of a series of lake deposits, 

 sands and clays, probably formed as a delta at the mouth of a large 

 river. They are more than 186 feet in thickness at some points, 

 and at least 18| miles wide along the shore of Lake Ontario ; while 

 they have been traced inland more than 6 miles, beyond which they 

 are buried under glacial materials. 



At the base of the series, resting on an eroded surface of Boulder- 

 clay, are 41 feet of the Don beds, containing, according to Professor 



1 Translation by Dr. F. A. Bather : Geol. Mag., May, 1901, pp. 205-216. 



2 "Glacial and Interglacial Beds near Toronto" : Journ. Geol., vol. ix, No. 4, 

 pp. 285-310. 



