G. F. WRIGHT — POST-GLACIAL OUTLET FROM GREAT LAKES. 425 



its present mouth. The bed is well-defined, with its bottom about 25 or 30 feel 

 above the present river and with bowlders of the largest size upon cadi side. 



Upon the north side of the Mattawa river for a mile or more above its junction 

 there is a slender but well-defined terrace of the same height with that upon the 

 south side, but consisting of fine material, presenting an area, which has naturally 

 been chosen for the cemetery and for a race-course. On the south side also the 

 great bowldery delta terrace shades into liner material higher up the stream. 



We followed up the Mattawa river a distance of about 8 miles, to the vicinity of 

 Eau Claire. Though not able to study the region so carefully as we would have 

 [iked, everything so far as we could observe was favorable to the theory of its 

 havingbeen the temporary channel of a great stream of water. Terraces exist here 

 and there, such as would be expected, and the descent of the channel at the portage 

 of Plain Champ would aid in producing that final plunge in the descending stream 

 required to produce the effects described at the junction a mile or more below. 



The only theories worth considering in accounting for these phenomena are that 

 this collection of bowlders is of the nature of a moraine modified by temporary 

 local floods which came down the Mattawa upon the melting of the ice, and that of 

 Mr Gilbert, that the torrent of Niagara was for a time diverted down this trough. 



The moraine theory would seem untenable from the position of the material. 

 It is not in position for a moraine moving down either the valley of the < Htawa or 

 of that of the Mattawa. It is in fact midway between the two, upon the lower 

 angle of their junction, and runs up the Mattawa valley in a way to indicate the 

 predominant influence of rushing water coming down that valley. The position 



and character of the bowlder terrace and its relation to the terrace upon tl ppo- 



site side of the Mattawa is strictly analogous to that which 1 have described* as 

 occurring at Beaver, Pennsylvania. The accumulation of bowlders is also strictly 

 analogous to that at Pocatello, Idaho, where the Port Neuf valley opens out into 

 the Great Snake River plain, and described by me on pages 235 236 of my recent 

 work, "Man and the Glacial Period." In the case of the beaver terraces we have 

 to account for them by the vast Hoods at the close of the Glacial Period, hut the 

 accumulation is as nothing in comparison with that at Mattawau. At Pocatello, 

 however, some time after my collection of the facts, the publication of Mr Gil- 

 bert's monograph upon Lake Bonneville made it (dear that the overflow of that 

 great lake led down the Port Neuf river, and that for a period of 25 years the 

 volume of the flow was comparable to that of the Niagara, and the results are, as 

 we have said, closely analogous to those at Mattawau and almost equal in their 

 extent. The further prosecution of inquiries through the whole length of the 

 valley of the Mattawa will, however, by some be thought necessary to complete 

 the verification of this theory ; but for one 1 expect, most confidently the evidence 

 will be forthcoming when attention is sufficiently directed to the region, 



Professor Wright's paper was discussed by the President and by Robert 



Bell. Dr Bell said: 



I have been over the ground referred toby Professor Wright and Mr Gilbert. I 



think Professor Wright's hypothesis interesting as a suggestion, but do not < - 



sider that sufficient evidence has yet been offered to make it anything more than 

 that. The matter has not been sufficiently investigated to enable us to c e to 



'■■ Bull. 58, U, S. Geoli Survey, p. 77, 



