GEOLOGY. 307 



will to a certain extent hold good; but in the analyses, by Dr. Streng, of 

 the volcanic rocks of Hungary and Armenia, we often find that the actual 

 proportions of alkalies, lime, and magnesia vary considerably from those 

 deduced from calculation. This will necessarily follow when feldspars, like 

 albite or anorthite, replace the labradorite in pyroxenic rocks. The phono- 

 lites are moreover highly basic rocks, which contain but very small amounts 

 of lime, magnesia, or iron, being essentially mixtures of orthoclase with 

 hydrous silicates of alumina and alkalies. 



IV. In a recent inquiry into the chemical conditions of a cooling globe 

 like our earth, I have endeavored to show that in the primitive crust all the 

 alkalies, lime, and magnesia, must have existed in combination with silica 

 and alumina, forming a mixture which perhaps resembled dolerite, while 

 the very dense atmosphere would contain, in the form of acid gases, all the 

 carbon, chlorine, and sulphur, with an excess of oxygen, nitrogen, and wa- 

 tery vapor. The first action of a hot acid rain, falling upon the yet uncooled 

 crust, would give rise to chlorides and sulphates with separation of silica; 

 and the accumulation of the atmospheric waters would form a sea charged 

 with salts of soda, lime, and magnesia. The subsequent decomposition of 

 the exposed portions of the crust, under the influence of water and carbonic 

 acid, would transform the feldspathic portions into a silicate of alumina 

 (clay) on the one hand, and alkaline bicarbonates on the other; these, de- 

 composing the lime-salts of the sea, would give rise to alkaline chlorides and 

 bicarbonate of lime the latter to be separated by precipitation, or by 

 organic agency, as limestone. In this way we may form an idea of the 

 generation from a primitive homogeneous mass, of the siliceous, calcareous, 

 and argillaceous elements which make up the earth's crust, while the source 

 of the vast amount of carbonate of lime in nature is also explained.* 



When we examine the waters, charged with saline matters, which impreg- 

 nate the great mass of calcareous strata constituting, in Canada, the base of 

 the Silurian system, we find that only about one-half of the chlorine is com- 

 bined with sodium ; the remainder exists as chlorides of calcium and mag- 

 nesium, the former predominating, while sulphates are present only in small 

 amount. If now we compare this composition, which may be regarded as 

 representing that of the palaeozoic sea, with that of the modern ocean, we 

 find that the chloride of calcium has been in great part replaced by common 

 salt, a process involving the intervention of carbonate of soda, and the 

 formation of carbonate of lime. The amount of magnesia in the sea, al- 

 though diminished by the formation of dolomites and magnesite, is now 

 many times greater than that of the lime; for so long as chloride of calcium 

 remains in the water, the magnesian salts are not precipitated by bicarbon- 

 ate of soda.t 



"When we consider that the vast amount of argillaceous sediment-matter 

 in the earth's strata has doubtlessly been formed by the same process which 

 is now going on, namely, the decomposition of feldspathic minerals, it is evi- 

 dent that we can scarcely exaggerate the importance of the part which the 

 alkaline carbonates, formed in this process, must have played in the chem- 

 istry of the seas. "We have only to recall waters like Lake Van, the natron 

 lakes of Egypt, Hungary, and many other regions, the great amounts of 



* Am. Jour. Sci. ( 2 ) xxv. 102, and Canadian Journal for May 1858. 

 t See Am. Jour. Science (2) xxyiii. pp. 170 and 305; Annual of Scientific Discov- 

 ery, 1859. 



