366 THE ICE AGE IN NORTH AMERICA. 



Mr. J. E. Marr, in recording his observations upon the 

 Jakobshavn Glacier, gives the following account of the gla- 

 cial dams connected with it : 



The Jakobshavn Glacier stops up both ends of a valley, 

 running parallel with its course, converting it into a lake, 

 which is separated from the glacier throughout the greater 

 part of its length by a nunatak.* The lower end of another 

 valley considerably to the south of this is stopped by the ice- 

 sheet, and the valley converted into a lake (Tasersiak), which 

 is drained by a river running over the col at the head of the 

 valley into the Strom Fiord, just as in the case of the Merjelen 

 See, only the Greenland lake is much larger than this. A 

 similar lake drains into the North Isortok Fiord, and another 

 into that of Alangordlia. Two similar lakes are formed to the 

 east of Sermilik Fiord, and several small ones to the east of 

 Bjornesund. North of the Frederikshaab Glacier is a valley 

 running north and south, the mouth of which is stopped by 

 the Frederikshaab Glacier, while a tongue of ice flows through 

 a col situated half-way up the valley and bars the valley, one 

 part of the tongue of ice flowing a small distance to the north 

 and another to the south, thus causing the conversion of the 

 valley into two lakes. On the east of the Frederikshaab Gla- 

 cier is the Lake Tasersiak, bounded on the north by the 

 nunatak Kangarsuk, and stopped at its lower end by the Fred- 

 erikshaab Glacier, and having a tongue of the ice-sheet en- 

 tering into it at the upper end. \ 



With these facts concerning existing glacial dams in 

 mind, we are prepared to study the signs of similar obstruc- 

 tions, on a larger scale, which occurred during the progress 

 of the Glacial period. We will first present the facts relat- 

 ing to a supposed obstruction by glacial ice, of the Ohio 

 River at Cincinnati. 



In the summer of 1882, after having the previous year 

 completed, with Professor Lewis, the exploration of the gla- 



* See p. 79. 



f " Geological Magazine " for April, 1887, quoted in the " American Journal 

 of Science," vol. exxxiv, 1887, p. 313. 



