556 TEE ICE AGE IN NORTH AMERICA. 



hundred and seventy-five feet, as shown by the deep well at the 

 Lake wood Cemetery. This would show that probably the an- 

 cient valley of the Minnesota where it passes Fort Snelling, 

 and all the way through Eamsey county and below, has been 

 filled more than two hundred feet by drift that originated 

 since the excavation of the gorge. This supposition is borne 

 out by all borings that have been made between the rock-bluffs 

 at lower points, as at West St. Paul and at Lake City. Such 

 excavation is not found in the river-gorge between Fort Snel- 

 ling and the Falls of St. Anthony ; but, below the water, are 

 found, first, some large fragments of limestone, and some bowl- 

 ders of foreign origin, the whole being generally less than 

 twenty-five feet in thickness, and below that the undisturbed 

 St. Peter sand-rock is found, suitable for the foundation of 

 piers for bridges. 



These facts warrant the conclusion that that part of the 

 Mississippi gorge above Fort Snelling has been excavated by 

 the recession of the falls since the last general drift movement, 

 and that prior to that event there was a gorge which passed 

 from the present channel of the Mississippi at the mouth of 

 Bassett's Creek southward to the great gorge of the Minnesota 

 at some place above Fort Snelling. It is probable that this 

 gorge was then occupied by waters that drained from the 

 northern part of the State, and had existed through many ages, 

 dating back to pre-Cretaceous times. It seems to have been 

 filled first by a blue till, or partly filled, and to have remained 

 free for the passage of the Mississippi during the on-coming of 

 the Glacial epoch, till the advent of the ice of the last Glacial 

 epoch, when morainic accumulations so choked it that the 

 water of the river was driven out and compelled to seek an- 

 other passage to the Minnesota. When this last event took 

 place, the Falls of St. Anthony probably began at Fort Snel- 

 ling, the water being precipitated over the rock-bluff of the 

 pre-existing old gorge, unless the whole valley was too deeply 

 buried under water. Whether this was at the beginning or at 

 the acme of cold, or at the recession of the ice, is a question 

 which may well be considered, but at this time the only point 

 that is claimed is that it was not earlier than the beginning of 

 the last Glacial epoch, and was probably near the acme of cold. 



