September 7, 1888.] 



SCIENCE. 



319 



was again excavated, perhaps to a greater depth than 

 the present river, possibly to the bottom of tlie gravel 

 and sand, at a point in tlie valley which is l.")0 feet 

 below the river (liere, and 135 feet below low water 

 in the Mississippi at St. Paul. 



When the ice-barrier which had made Lake Agassiz 

 disappeared, that lake was drained northward toward 

 Hudson bay. Thenceforward, the rivers of the Min- 

 nesota and Mississippi valleys carried only a fraction 

 of the former volume of water from this source. 

 They have since become extensively filled with al- 

 luvial gravel, sand, clay, and silt, brought in by the 

 tributaries of those rivers. The changes produced 

 by this post-glacial sedimentation have been ably dis- 

 cussed by Gen. G. K. Warren, and were briefly sum- 

 marized in the paper of Mr. Upham. 



Lake Superior seems to have been held by an ice- 

 barrier at a level of about 5tin feet from its present 

 height. The locality of its overflow was stated, and 

 various results detailed. Lake Michigan, until the 

 ice-sheet receded from its northern border, dis- 

 charged southward by the Illinois river, which, like 

 the former outlet of Lake Superior, was eventually 

 obstructed by alluvium, so that now it has a very 

 slight current for two hundred miles. 



The paper closed with a proposition to call the 

 ancient river of the glacial age, the river Warren, in 

 honor of Gen. G. K. Warren. 



The discussion which followed was, in part, a con- 

 flict between the glacialists and their opponents, and, 

 in part, a debate upon the general question of nam- 

 ing geological features after distinguished investi- 

 gators. 



Changes in the currents of the ice of the last 

 glacial epoch in eastern Minnesota. 



BV WAUREN UPn.VM OF MIX.NEAPliLlS, .MINN. 



WiTHOOT a map, or a thorough familiarity with 

 the region referred to, this paper would not convey 

 very definite ideas. Througli some inadvertency tlie 

 map intended to be used was not on hand when the 

 paper was read. The author's observations had led 

 him to conclusions of a very definite character. He 

 conceived, that, when the ice of the last glacial epoch 

 attained its maximiun extent, there were two ice- 

 currents. One moved south-westerly from Lake 

 Superior, across the north-east part of Minnesota, 

 spreading a reddish till with bowlders and pebbles, 

 .and limited by a line from Lake St. Croix south-west 

 .across the Mississippi, and thence bending north- 

 west by Lake Minnetonka, and through Wright and 

 Stearns counties. The other portion of the ice-sheet 

 was pushed from the region of Lake Winnipeg, south 

 and south-east. The two met along a line from 

 Stearns county, south-east by Lake Minnetonka to 

 Crystal Lake, Dakota county. Afterward, when the 

 ice had partly melted and retreated, a second and 

 inner terminal moraine w.as formed. Owing to cli- 

 matic changes (the rationale nf which was carefully 

 and very explicitly set forth in the paper), the current 

 from the north-west pushed back that from the east, 

 and covered the reddish till, already deposited, with a 



blue till from the west and north-west, also abundant 

 in its peculiar bowlders and other evidences of its 

 source. 



The kame rivers of Maine. 



BY O, H. STONE OF COLORADO SPKINOS, COL. 



Lv the absence of its author, this paper was read by 

 -Mr. Upham. After defining and describing the char- 

 a<'teristics of kanies, and stating that they are very 

 numerous in Maine, where he had observed them, the 

 author proceeded to discuss a single question in rela- 

 tion to these geological features. Most glacialists are 

 .igreed that the kame gravels of the drift region were 

 chiefly deposited by glacial streams. The question is, 

 whether these streams were sub-glacial or super-gla- 

 cial. In exploration during the past five years, the 

 author had found evidences of both kinds of streams; 

 l)Ut he nowhere found stratified or even water-classi- 

 fied material enclosed in this formation, except within 

 a few miles of the coa-st. 



The essayist sought to answer the question by con- 

 sidering the processes of melting which take place in 

 a glacier. Strict an.alogy with existing glaciers — even 

 with those of Greenland — should not be supposed. 

 In modern glaciers, nearly all the water of their lower 

 extremities is sub-gl.acial. The ice is so broken by 

 crevasses that melting waters soon find their way to 

 the bottom. IJut a different state of affairs may have 

 prevailed in the continental glacier. Sever.al of these 

 kame rivers are a hundred or more miles in length. 

 Granting all reasonable development of sub-glacial 

 streams, these kames can scarcely be thus accounted 

 for. Superficial water flowing along the surface 

 would gradually deepen its channel: when the melt- 

 ing had so far proceeded that the bottoms of these 

 streams reached the mor.aine stuff in the lower part 

 of the ice, the kame gravel would begin to gather on 

 the bottoms of their channels. During the final melt- 

 ing, when the condition was such that few if any ad- 

 ditional crevasses would be formed, there would be 

 no time to extend the previously formed sub-glacial 

 channels. The sudden floods would pass over the 

 lowest part of the ice as they would over groutid. A 

 great and rapid northward extension of the superfi- 

 cial streams would result. 



In discussing this p.aper, Mr. Upham stated that 

 erosion does not appear in kames. They are not un- 

 frcquently a hundred feet in height: one on the bor- 

 ders of the Merrimac river was instanced. They 

 appear to be gravel deposits laid down before the 

 glacier was fully melted. 



Relation of the glacial dam at Cincinnati to 

 the terrace in the upper Ohio and its tribu- 

 taries. 



BY I. C. WHITE OF .MOROANTOW.V, W. VA. 



Tuis paper, in the absence of its author, was read 

 by Professor Winchell. 



In a paper read before the Boston society of natu- 

 ral history, March 7, 18S3, Rev. G. F. Wright showed 

 that the southern rim of the great northern ice-sheet 



