232 



REPORT OF NATIONAL MUSEUM, 1904. 



to the northward, while the region to the southward was dry land. A 

 tittie came, however, when the dams at various points proved too frail 

 and gave way, the pent-up waters rushing through and carrying 

 devastation with them like the waters from cloud-bursts or bursting- 

 reservoirs of to-day, but on a thousandfold larger scale. 



One breach was conceived to have been at the northeastern extremity 

 of Lake Ontario. The Thousand Isles, to Mitchill's mind, " bear wit- 

 ness to the mighty rush of waters which thus prostrated the opposing 





*r*J l \ n \<+ — --^ w/r 1 



Fig. 4.— Map to illustrate Mitchill's theory of barriers 



mound and left them as scattered monuments of the ruin." "By this 

 operation the water must have subsided about 160 feet,"" or to its 

 present level. 



All the country on both the Canadian and Fredonian sides must have been drained 

 and left bare * * * exposing to view the waterworn pebbles, the works of marine 

 animals, their solid parts buried in the soil, their relicks bedded in the rocks, and the 

 whole exhibition of organic remains formed in the bottom of such a sea as that was. 



Great masses of primitive rocks from the demolished mound or dam and vast 

 quantities of sand, mud, and gravel were carried down the stream to form the 

 curious mixture of primitive with alluvial materials in regions below. 



