WHOLE VOL. SKELETAL REMAINS OF EARLY MAN HRDLICKA 1 7 



Basin at less than 10,000 years ago. This being the case the ice sheet persisted 

 west of Hudson Bay down to that time. It is probable that the ice sheet on the 

 Labrador peninsula persisted down to fully as late a time as that west of 

 Hudson Bay. 



I have written very little concerning the chronology of the glacial epoch, 

 though I have had considerable correspondence with other glacialists on the 

 subject. I differ from some of them in thinking that there was a prolonged 

 period of extensive glaciation in the Wisconsin or latest glacial stage. I find 

 that the ice sheet continued to grow westward long after the Labrador part had 

 reached its limit at the Shelbyville moraine. As a result the extent or area of 

 the ice sheet may have been greater in what is known as Late Wisconsin time 

 than in the time of the Shelbyville moraine, though its eastern part had shrunk 

 considerably by that time. I am inclined to make the culmination of the ice 

 sheet cover a longer time than that involved in its growth to the Shelbyville 

 moraine. I think the majority of the glacial students, here and in Europe, would 

 make the last glacial stage cover a period of 74,000 to 100,000 years. I think at 

 least 40 per cent of this stage should be allotted to the culmination, and 30 per 

 cent or less to growth to the Shelbyville moraine, and a similar per cent to the 

 departure of the ice sheet, the departure following the development of the Port 

 Huron morainic system (see Monograph 53, U. S. Geol. Survey, for the place 

 of this morainic system). 



As to earlier glacial stages, the time involved seems likely to be similar to tiiat 

 involved in the Wisconsin stage as the extent or area covered was but slightly 

 different from that covered in the Wisconsin stage. 



The period between the Illinoian, or third glacial stage, and the Wisconsin, 

 or last glacial stage, seems to be somewhat longer than that involved in either 

 of these glacial stages. The basis for estimates is the relative amounts of erosion 

 and weathering each drift has suffered. On this basis it seems safe to put the 

 culmination of the Illinoian at not less than 200,000 years ago. 



On the basis of the amount of weathering and erosion displayed by the next 

 older drift, the Kansan, it seems likely to date back at least a half million years. 

 The Nebraskan, or first drift, is much older, but is so largely buried under the 

 later drifts that one cannot well estimate its relative age. But I think it safe to 

 say that it dates back not less than three fourths of a million years. 



I trust you will not take these estimates as at all exact in a mathematical sense. 

 They are intended to merely express the general relations in time, though they 

 are based on a study carried on for more than forty years. 



Very truly yours, 



(Signed) Fr.\nk Leverett. 

 Dr. Antevs' 



AMERICAN GEOGRAPHICAL SOCIETY 



Broadway at 156TH Street, 



New York, N. Y., 



Nov. 7, 1928 



Dr. Hrdlicka : 



I listened with great interest to your lecture in the American Museum of 

 Natural History last Monday and got a much more vivid idea of several prob- 



