Revieics — W. Upham^s Lake Agassiz. 229 



part were being deposited, the northern part was still covered by 

 the ice, and before this district was submerged the opening of the 

 northern outlets had so lowered the water-level that the southern 

 shore had followed the ice to the north. With the final disappear- 

 ance of the ice-sheet, Lake Agassiz was reduced to a series of 

 scattered lakes, of which Lake Winnipeg is the largest. 



The ordinary Glacial drifts of the district are attributed to the 

 action of land-ice, as there is no sign of any transport in or assort- 

 ment by water. The maximum thickness is 250 feet; the lower 

 part is very hard and tough, but the upper beds are fairly loose and 

 can be dug. The author attributes the difference to the former 

 having been subjected to the enormous pressure of the weight of 

 the ice-sheet, while the latter was merely dropped during the 

 melting of ice. There are many boulders mainly of the Archaean 

 rocks from the N. and N.E. ; the largest is 22 ft. by 8 ft. by lift. 

 Striae are well preserved and their directions are given in an 

 appendix. The more especially lacustrine deposits include a series 

 of sixteen beaches ; these are from 25 to 30 rods in width, and rise 

 from 3 feet to 10 feet on the shore side, and from 10 feet to 20 feet 

 on the lake side. There are also a number of deltas and kames and 

 osars : the author uses the two last terms as defined by McGee and 

 Chamberlin ; he applies "osars" to the drifts formed in the river- 

 courses, and "kames" to the irregular deposits dropped where the 

 rivers have emerged from between their ice-walled channels and 

 spread out over the adjoining lowlands. 



A few freshwater Mollusca of existing species have been found, 

 and some worked flints indicate that man lived on the shores of the 

 lake before the opening of the northern outlets. But the author, 

 quoting a long series of independent estimates, considers that this 

 was less than 10,000 yeai's ago. 



It is found that the beaches ascend as they are traced to the North, 

 the amount varying from one to sixteen inches to the mile : he con- 

 cludes — accepting Mr. R. S. Woodward's calculations — that a quarter 

 of this was due to the heaping-up of the water by the attraction of 

 the northern ice-sheet. After a careful consideration of Chamberlin's 

 hypothesis of alterations of level being due to contraction of the earth's 

 crust consequent on the lowering of the isogeotherms by a glacial 

 climate, it is rejected as inadequate, as its influence would be the 

 reverse of that which has taken place in the Lake Agassiz area. 



The memoir closes with a chapter on the " Geologic and Agri- 

 cultural Resources " of the district. It is illustrated by a couple of 

 maps and a plate of sections ; but further illustrations will no doubt 

 be given with the more detailed description to be given by the 

 author in one of the Monographs of the United States Geological 

 Survey. The exploration, it should be added, was undertaken, on 

 behalf of the Geological Surveys of the United States and Canada, 

 both of which may be congratulated upon an arrangement whereby, 

 in defiance of International Boundaries, the whole work was entrusted 

 to one man, and also upon having secured the services of a geologist 

 whom a long training in glacial geology had rendered especially 

 competent for the task. J. W. G. 



