Proceedings of the British Association. 141 



this course thickly studded with well- wooded islands, amongst which 

 the waters of the river flowed. Upon a level with the surface of these 

 islands were extensive plains connected occasionally with lateral val- 

 leys coming through the escarpments, the soil of which was iden- 

 tically the same with that of the islands, being a light vegetable sandy 

 soil much mixed up with decayed freshwater shells ; showing that 

 these soils were the old muddy bottom of the river, deposited 

 when it occupied the whole breadth of the valley from escarpment to 

 escarpment. These, and analogous appearances upon the courses of 

 other American rivers, especially the immense lacustrine deposits 

 separating Lake Erie from Lake Huron, seventy miles in breadth, 

 were adduced as proofs of a great diminution of the quantity of fresh 

 water once occupying the lakes and the fluviatile courses of that 

 continent ; indeed, from the difference of level between a point on the 

 Wisconsin River and the channel of the upper Fox River, over which 

 boats now pass in time of great floods, the water communication 

 betwixt the Mississippi and Lake Erie seems to have been uninter- 

 rupted. This portion of the paper was intended to show, that 

 the quantity of water in the rivers in ancient times so far exceeded 

 the quantity flowing in them at present, that the cataracts in the 

 rivers must have been much more powerful, and that therefore 

 the process of excavation of the rocky channels of rivers by the 

 recession of their cataracts, must have been then effected in much 

 shorter periods of time than at present. From all these considera- 

 tions, and from the known fact that the Falls of St. Anthony had not 

 receded more than twenty yards in the last 100 years, the author 

 drew the deduction that the whole valley of the Mississippi, from the 

 falls of St. Anthony to the point where the escarpments terminate, 

 had been excavated by the recession of that cataract, and that the 

 excavation had proceeded at a much more rapid pace than it does in 

 our times. The author next proceeded to explain the peculiar me- 

 chanical power which streams employ in forming their channels by the 

 operation of cataracts, and divided it into two methods, the molar or 

 grinding process, most common in mountainous countries constituted 

 of primary rocks and the subtracting or undermining power exercised 

 upon strata of a softer quality. To illustrate the first of these 

 methods, Mr. Featherstonhaugh exhibited a beautiful pictorial view 



