236 ANNUAL OF SCIENTIFIC DISCOVERY. 



to three per cent. The author inquires, "To what cause are we to 

 assign the changes that have taken place? Has the magnesia been 

 sublimed by heat ? or has it been withdrawn by the solvent power of 

 free carbonic acid ? The subject is one of great interest, both to the 

 geologist and chemist, as the facts are directly opposed to the received 

 views, and as no instance of similar changes on dolomitic rocks has, 

 so far as I am aware, been put on record." 



DECOMPOSITION OF ROCKS. 



M. EBELMEN, at the conclusion of a memoir on this subject, ex- 

 amines one of the most important questions relating to the natural 

 history of the globe, that of the relations which necessarily exist 

 between the phenomena of the alteration of rocks, and the composi- 

 tion of atmospheric air. " The different bases which separate from 

 the silex by the decomposition of igneous rocks determine, in fact, 

 the precipitation, the mineralization of the oxygen and of the carbonic 

 acid ; the last element in particular is absorbed in great quantity, and 

 a simple calculation shows that a small body of decomposed plutonic 

 rocks is sufficient for the complete precipitation of the carbonic acid 

 contained in the air. Now, the argillaceous bed of stratified forma- 

 tions induces the decomposition of immense masses of plutonic rocks ; 

 and, consequently, the precipitation of quantities of carbonic acid out 

 of all proportion with those actually existing in the atmosphere. 

 This result may be explained without any necessity of admitting that 

 the air has possessed, in the different geological epochs, a very differ- 

 ent composition from that which it now presents. 



" I observe in volcanic phenomena," says M. Ebelmen, " the prin- 

 cipal cause which restores to the atmosphere the carbonic acid which 

 the decomposition of rocks continually precipitates from it. We 

 know that this gas is disengaged in abundance from the ground in the 

 neighbourhood of active volcanoes, and even from extinct volcanoes. 

 It is interesting to witness the formation of igneous rocks, accom- 

 panied with the disengagement of a gas, which the destruction of 

 these same rocks will precipitate. The central heat of the globe 

 will, therefore, be indispensable for the maintenance of organic life on 

 its surface. The beautiful experiments of Saussure on the influence 

 of the carbonic acid of the air on the nourishment of vegetables, are 

 no longer sufficient to explain the permanence of the composition of 

 atmospheric air. We see that phenomena entirely of a different kind 

 must be introduced for the solution of the question, and that the 

 mineral elements of the crust of the earth likewise concur, by the 

 inverse reaction, the one on the other, to produce this equilibrium." 

 LSInstitut. 



THE DEAD SEA. 



THE following interesting facts are from Lieutenant Lynch's Official 

 Report of the Exploring Expedition to the Dead Sea : 



" The bottom of the northern part of the Dead Sea is almost flat (a 

 plain). The meridional lines at a short distance from the shore vary but 



