26 DE. THOMAS STEERY HUNT ON THE 



many years, to define and classify the rocks of the first two of these classes, and by ex- 

 tended studies in Europe, as well as in North America, sticceeded in establishing an 

 order, a succession, and a nomenclature, which are now beginning to find recognition on 

 both continents/' 



"While the succession of the various groups of crystalline rocks was thus being esta- 

 blished, not without the efficient aid and co-operation of other workers in late years, min- 

 eralogical and chemical stiidies were teaching us much of the true nature of the diffe- 

 rences and resemblances of these groups, as well as of the natural relations and modes of 

 formation of various silicates and other mineral species which enter into the composition of 

 the crystalline rocks. The investigations of physicists and astronomers had moreover 

 given form and consistence to the ancient theory of the igneous origin of our planet, and 

 the concurrent working in all of the lines of investigation above indicated was thus pre- 

 paring the way for a new hypothesis of the origin of crystalline rocks — a hypothesis 

 of which I shall endeavou.r to sketch the growth and the evolution. 



§ 50. It was in January, 1858, more than a quarter of a century since, that I ventured 

 to put forth a speculation as to the chemistry of a cooling and still molten globe. Consi- 

 dering only that crust with which geognosy makes us acquainted, it was maintained that 

 at a very early period the whole of its non-volatile elements were united in a fused mass of 

 silicates, which included the metallic bases of the salts now dissolved in the ocean's waters ; 

 while the dense atmosphere of that time was charged with all the carbon, sulphur, and 

 chlorine, combined with oxygen or with hydrogen, besides which were present watery 

 vapor, nitrogen, and a probable excess of oxygen. The first precipitated and acid waters 

 from this atmosphere falling on the hot earth's silicated crust, would, it was said, soon 

 become neutralized by the protoxyd bases, giving rise to the chlorids and sulphates of the 

 primeval sea ; with the probable separation of the combined silica, at that high tempera- 

 ture, in the form of quartz. The suggestion as to the acid nature of the primitive 

 atmosphere, and its first chemical action, which were obvious deductions from the igneous 

 theory, had, as I afterwards learned, been anticipated by Quenstedt.^* 



§ 51. These views were reiterated in May, 1858, when they were coupled with the 

 conception of a solid nucleus to the globe as then taught by Poulett Scrope and by Wil- 

 liam Hopkins. The subsequent subaërial decay of exposed portions of the earth's primi- 

 tive crust in a moist atmosphere, now purged of the acid compounds of chlorine and 

 sulphur, but still holding carbonic acid, was then set forth as resulting in the transforma- 

 tion of feldspathic silicates into clays, and the transference to the sea of the lime, magnesia 

 and alkalies of the decayed rock in the form of carbonates, the latter of which, reacting on 

 calcium-chlorid, would yield carbonate of lime and chlorids of sodium and magnesium. It 

 was then said that by this hypothesis " we obtain a notion of the processes by which, from 

 a primitive fused mass, may be generated the various silicious, argillaceous and calcareous 



" I have elsewhere given the history of the progress of inquiry in this direction in Report E of the Second 

 Geological Survey of Pennsylvania (Azoic Rocks) 1878 ; in brief, in an essay on Pre-Cambrian Rocks, etc., in the 

 Amer. Jour. Science, 1880, (xiv. 268) ; and later in a study of the Pre-Cambrian Rocks of the Alps, in the Trans. 

 Roy. Soc, Canada, vol. i, part 3, pp. 182-196. See also in this connection the late address of Dr. Hicks, 

 president of the British Geologists' Association, in its Proceedings, vol. viii. 1SS3, On the Succession of the Archaean 

 Eocks, etc. ; and the still more recent paper of Prof. Bonney, president of the Geological Society of London, on The 

 Building of the Alps, in Nature for May 18 and 25, 1884 ; also the Geological Magazine for June 1884, p. 280. 



" Epochen der Natur. p. 20. 



