258 American Association. 



as tlie Laurentian series. These local names are, of course, onh- 

 provisional, devised for the purpose of avoiding periphrastic or 

 descriptive titles, the use of vrhich has been found inconvenient ; 

 and they can be changed "when more important developements, 

 proved to be the equivalents of the series, are met with elsewhere. 

 In answer to a question whether these Huronian Rocks were 

 older than the Silurian, or whether there was any indication of 

 their being Silurian metamorphosed ; Sir William said the Hu- 

 ronian rocks lie unconformably under the Silurian, and that the 

 lower beds of the Silurian in contact with the Huronian are made 

 up of its ruins. They found the Huronian in nearly a vertical 

 attitude, but there is no possibility of doubt as to the comparative 

 age of the Huronian and Silurian rocks.'' 



ORIGIX OF MAGNESIAS K0CK3. 



Mr. T. Sterry Hunt then read a very interesting paper on 

 Mineral Waters and on the origin of Z\Iagne3ian Eocks. " He allud- 

 ed first to the deposits of mineral springs and especially of 

 calcareous waters, as having played an important part in the for- 

 mation of rocks. The deposits of such waters are however gene- 

 rally destitute of carbonate of magnesia, which is held in solution 

 by them, and only precipitated on evaporation. Carbonate of 

 soda is very abundantly distributed in certain mineral waters, and 

 these mingling with sea-water, or with mineral waters analogous 

 to it in their nature, have at first the eflect of eliminating the lime 

 as a carbonate, leaving the greater part of the magnesia in solution, 

 ready to be precipitated in part by evaporation, or more completely 

 by the farther addition of carbonate of soda. In this way dolo- 

 mites may be deposited in the open sea, and may form, as they 

 often do, the cementing material of conglomerate or coralline lime- 

 stones. They may be equally formed by the evaporation in limited 

 basins or lagoons, of waters holding carbonate of magnesia dissolved 

 in the manner above described ; in the latter case, we can easily 

 understand the precipitation of magnesian carbonate unmixed with 

 lime. The interstratification of dolomites with pure limestones in 

 the Silurian rocks of Canada, was described as irreconcilable with 

 the hitherto received theories of the origin of dolomites, and it was 

 maintained that the hypothesis now proposed, is the only one 

 which meets the conditions of the problem."' 



SUBSIDENCE OF LAXDS. 



Professor G. H. Cook, of Eutger's College, then read a paper 

 on the subsidence of the land on the sea coast of J^ew Jersey and 



