358 A. P. Coleman — Wave Work as a Measure of T\ 



%me: 



far as the Toronto region, so that wave work conld be^in at 

 Scarboro', is very hard to estimate. The guess hazarded in my 

 last paper, that the events occurring in the interval between the 

 two lakes might require about 8,000 years, is objected to by 

 Dr. Spencer, who thinks the time much too short. In this he 

 may be right, in which case the 8,000 years suggested should 

 be looked upon as a minimum ; and the whole period since the 

 ice left the Ontario basin may be considered to have been at 

 least 24,000 years, but probably somewhat longer. 



There are two other points of interest raised in Dr. Spencer's 

 paper, that of the constancy of level in Lake Ontario in recent 

 times ; and that of the limit to be assigned for the end of the 

 ice age. These may be discussed briefly. 



He suggests that '"'researches as to the great accession of 

 water to the Niagara river show that the terrestrial tilting 

 about the northeastern angle of Lake Huron occurred as late as 

 3,500 years ago. Tliis earth movement extending to the St. 

 Lawrence river was that which gave birth to the great modern 

 river itself. No appreciable deformation has since occurred. 

 Consequently Lake Ontario is found to be some 3,500 years 

 old." 



The fact that all the streams flowing into Lake Ontario near 

 the southwestern end have dead water for two or three miles 

 while their courses are rapid above this point, strongly sug- 

 gests that the water has been backed up by the differential 

 elevation of the outlet of the lake ; and the further fact 

 that the lagoons behind the meanders are not yet filled up with 

 mud from the spring floods, nor with peat or other vegetable 

 matter, suggests that the change of level has been much more 

 recent than 3,500 years. 



The other point is raised in the following rather curious 



manner : " the professor has shown elsewhere that 



Lake Iroquois was a glacial lake, consequently his 8,000 years 

 as the age of the Iroquois beach must be taken away from his 

 post-glacial time, leaving 16,000 years. Such a priori philoso- 

 phy leaves a suspicion that its author had some speculation to 

 support, but the analyses of the data show that a confusion is 

 thereby thrown into the problem of geological time when he had 

 within his grasp the material for a lasting scientific contribu- 

 tion of great value, and if the confusion be not expunged 

 such must lead to the retardation of scientific research." 



The suspicion suggested that I had ''some speculation to 

 support" need not be replied to, but the question as to when 

 one geological period ends and another begins is of consider- 

 able interest. When did the Glacial Period end ? When the 

 ice began to disappear, when it had half disappeared, or when 

 it had wholly disapj)eared? If the last assum.ption is made the 



