PHYSICS AND NATURAL HISTORY OF GENEVA. 1S3 



of masses of ice more or less considerable, wliich rise and float on the surface of 

 the Avater. The analysis of M. I*lautamonr has been inserted ia the Archives 

 of the Bibliothcque Vnivcrsdlc. 



Chemistry. — Memoirs. — Professor Marignac communicated to the society the 

 continuation of his researches on the silico-tungstates. He has recognized three 

 distinct acids formed by the combination of tungstic acid and silicic acid, namely : 

 1st. Silico-tungstic acid, containing 1^ equivalents of tungstic acid for 1 of silicic 

 acid; 2d. Silico-decitungstic acid, 10 equivalents of tungstic acid for 1 of silicic 

 acid; 3d. Tungsto-silicic acid, which has the same composition as the first, but 

 which differs by its crystalline form. He remarks that a great number of salts 

 of these acids present crystalline foims almost identical, although not by any 

 means so in their composition. This fact seems to him to indicate the necessity 

 of admitting the following extension of Mitscherlich's principle of isomorphism, 

 viz : that two compounds including an element or a group of common elements, 

 which constitutes by much the greater part of their weight, viay he isomorphous, 

 even when the elements in which they differ do not constitute by themselves an 

 isomorphous group. M. Delafontaine read a memoir on the atomic weight of 

 thorine or thorium. He has repeated the analysis of the sulphate of thorium 

 after the method of Berzelius. The moan of several accordant results yielded 

 him for the equivalent of thorine the figure 823.3, and admitting that the form- 

 ula of this is Tho^, the weight of its atom referred to oxygen would be 1,646.6, 

 and that of thorium 1,446.6. To the same author we owe a note on the place 

 which thallium should occupy among the elements. Several chemists place it 

 among the alkaline metals, wliile others consider it as being related to lead. Of 

 these two views our colleagixe adopts the former. 



Verbal reports. — M. Clusius has modified his theoiy on the atomic composi- 

 tion of ozone. It is not this body, it would seem, but oxygen which is formed 

 of atoms grouped two and two — atoms which are dissociated when oxygen passes 

 into the state of ozone. But it is objected to this new theory that ozone having 

 more density than oxygen, it is the former, not oxygen, which must be com- 

 posed of grouped atoms. 



NATURAL SCIENCES. 



Geology. — Memoirs. — M. Favre has continued his communications on the 

 geological constitution of the Chablais. The soil of this province is composed 

 of new formations superposed in the following order ; the glacial, fucoid schists, 

 kimmeridgian l.mestone, collovian limestone, liasian, lower lias, triassic, coal, and 

 serpentine. One of the characters of the region is the absence of cretaceous 

 and nummulitic formations ; an absence which results probably from the soil in 

 question having been already elevated above the surface of the water at the 

 epoch of the cretaceous and nummulitic seas. The author afterwards presents 

 a geological description of that part of Savoy traversed by the valleys of Me- 

 geve and of Haut-Lucc. Among other formations he there recognizes the black 

 slates of the Jurassic period, forming the crest of Mont Joli ; a fine deposit of 

 vegetable fossils of the carboniferous era, near Bonhomme ; and near Beaufort 

 deposits of anthracite. He also shows that the granitic group of Mont Blanc is 

 separated from that of Beaufort by sedimentary rocks, a continuation of those 

 of the valley of Chamounix, and thus the granite of Beaufort would seem to be 

 a prolongation of that of Valorsina. 



M. Favre also gave an account of an investigation in which he is engaged of 

 the deposits of translation between Jura and the Alps. These deposits present 

 four principal stages : 1st, the present alluvium ; 2d, the alluvium of the ter- 

 races, deposited by great currents of water above the glacial formation, and at a 

 maximum elevation of 30 to 33 metres above the lake ; 3d, the glacial deposit, 

 composed of loam, of rolled pebbles, and of some erratic blocks j 4th, the old 

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