164 THE CANADIAN NATURALIST. [Vol. vii. 



of limestones, and the Hudson group; the Latter forming the 

 summit of the Lower Silurian System. The Upper Silurian 

 System has at its base the Medina sandstone ; above this lie in 

 succession the Clinton, the Niagara, and the Helderberg groups. 



The Devonian system consists, in like manner, of the Oriskany 

 sandstone, the Schoharie grit, the Corniferous limestone, and the 

 Hamilton group. The carboniferous system, as Prof Newberry 

 claims, should begin with the Portage and Chemung, above 

 which are the Waverley, the Carboniferous Limestone, and the 

 Coal Measures. Now, if we compare these systems we shall see 

 that they consist of circles of deposition, first, sandstone, viz., 

 the Potsdam, the Medina, the Oriskany, and the Portage; second 

 mixed, mechanical, and organic sediments, viz., the Calciferous, 

 the Clinton, the Schoharie and the Waverley. ^ 



The third member of each group is a limestone, viz., the Tren- 

 ton, the Niagara, the Corniferous and the Carboniferous lime- 

 stone. The fourth member of each group is a mixture of 

 mechanical and organic sediments, viz., the Hudson, the Helder- 

 berg, the Hamilton and the Coal Measures. Prof. Newberry 

 claimed that each of the circles of sediments was formed by an 

 invasion of the land by the sea, producing, first a sheet of sea- 

 beach sand and gravel ; second, the ofi"-shore deposits following 

 and covering the first; third, the open sea calcareous, organic de- 

 posits — a limestone ; fourth, a mixed sediment — shale and lime- 

 stone, or an earthy limestone — the product of the retreating sea. 

 Between these submergences perhaps millions of years elapsed, 

 in which the fauna of the sea and the flora of the land were 

 changed. Hence the different fossils of the different systems. 



THE PROXIMATE FUTURE OF NIAGARA. 



By Prof. G. W. Holley. 



Prof. Tyndall said that if the rate of recession named by Sir C. 

 Leyell, a foot a year, was correct, in 5,000 years the Horseshoe 

 Falls would be far above Goat Island, and the American channel 

 would be dry. Prof. Holley showed that Sir Charles's rate was 

 the result of a conjecture founded on a guess. He also, by 

 means of the most trustworthy data we have since the commence- 

 ment of the historic period, showed that it would be more than 

 iwice that lensrth of time before the falls would recede a mile. 



