324 Scientific Intelligence. 



" It is also necessary at the same time to remember the chem- 

 ical relationship of carbon and silicon. Another point is, that in 

 all probability the first minerals produced by metamorphism are 

 elaborated from materials contained within the rocks themselves; 

 but eventually other constituents are added, or are removed, by 

 the circulation of water, by vapors, or by diffusion from neigh- 

 boring rock masses or igneous magma. Cossa found that he 

 could reproduce periclase by heating for some hours magnesic 

 sulphate and sodic chloride, and obtained still larger crystals by 

 adding a little ferrous sulphate. This, however, is hardly likely 

 to be the process of formation in the rocks beneath Vesuvius. 

 Deville reproduced periclase by acting on magnesia by hydro- 

 chloric acid gas, and Daubree by the action of magnesic chloride 

 on lime. There is good reason to believe that it was by one or 

 both of the latter processes that resulted in the production of 

 periclase in the magnesian limestone, especially when we take 

 into consideration the great abundance of hydrochloric acid and 

 chlorides contained within the neighboring incandescent lava of 

 Vesuvius. The artificial reproduction of fosterite by Ebelmen 

 probably is a near imitation of what occurred in its natural pro- 

 duction. 



" In fine, we see a definite order of chemical changes occurring 

 in Jurassic and Cretaceous limestone, which may convert that 

 rock into a granitic mass of crystallized basic silicates and oxides, 

 etc., which may in their turn by decomposition, give rise to a 

 group of rocks in which the original constituents would be repre- 

 sented by serpentine and its varieties, Tremolite, Brucite, etc., an 

 association which prevails amongst metamorphic rocks that are 

 exposed at the surface by that series of precai'ious events consti- 

 tuting denudation. 



" With regard to the removal of the lime in these metamor- 

 phosed rocks, Mierisch (loc. cit. p. 187) supposes the excess to 

 have been carried off as chloride by fumarolic action, and thinks 

 that the small quantity deposited around f umaroles proof of such 

 being the case. Without laying stress on the latter, we may 

 admit that this is very probable; may it not, however, be that 

 much of the lime is retained in the lava, being utilized in the for- 

 mation of some or all the lime-bearing crystal components, whilst 

 the HC1 would volatilize, as we know it does do, very largely 

 from the volcanic vent. 



" As Mierisch has to a great extent exhausted the description 

 of the drusy limestones, it is proposed in the next paper to treat 

 of the massive limestones, their alteration, metamorphism, and 

 their derivatives." 



The average elevation of the United States, by Henry Gannett, (extract from the 

 13th Ann. Rept. of the Diiector of the U. S. Geol. Survey, 1891-92. pp. 282-289 

 and colored Relief Maps of the United States. 



The Mechanics of Appalachian Structure, by Bailey "Willis. (Extract from the 

 13th Annual Report of the Directors. U. S. Geological Survey 1891-92, pp. 211- 

 281 and Plates nlvi-ncvi.) "Washington, 1894. 



