OEIGIN OF GEYSTALLIISTE EOCKS. 27 



rocks which make tip the greater part of the earth's crust." Of this it was declared, " the 

 earth's solid crust of anhydrous and j^rimitive igneous rock is everywhere deeply concealed 

 beneath its own ruins, which form a great mass of sedimentary strata, permeated by 

 water," and subjected to heat from below, changing them to crystalline metamorphic 

 rocks, and at length reducing them to a state of igneo-aqueous fusion, through which they 

 yield eruptive rocks. Of this primitive crust it was farther asserted that it " probably 

 approached to dolerite in composition." 



The principal points in this hypothesis, as presented in 1858, were thus the solid 

 condition of the earth's interior, and the derivation of the whole of the rocks of the known 

 crust, by chemical transformations, from the original superficial and last-congealed layer 

 of the cooling globe, which was considered to have been a basic rock, not unlike dolerite. 

 AU of these positions are fundamental to the present hypothesis. 



§ 52. These views were again repeated in a paper read before the Geological Society 

 of London in June, 1859, with some farther developments as to the origin of the various 

 crystalline rocks derived from the primeval crust. This, it was claimed, was necessarily 

 quartzless, and far removed in composition from the supposed granitic substratvim, or the 

 primitive gneiss. An attempt was, however, made to show that with the quartz, derived 

 from the supposed first decomposition of the primitive igneous rock by acid waters, and 

 the sediments resulting from subsequent disintegration and subaërial decay, coarser and 

 finer sediments, more or less permeable, would result, which by the natural chemical 

 action of infiltrating waters might, in accordance with known laws, divide themselves 

 into two great classes, " the one characterized by an excess of silica, by the predomin- 

 ance of potash, and by small amounts of lime, magnesia and soda, and represented by 

 the granites and trachytes ; while in the other silica and potash are less abvindant, and 

 soda, lime and magnesia i^revail, giving rise to pyroxene and triclinic feldspars. The 

 metamorphism and displacement of such sediments may thus enable as to explain the 

 origin of the difterent varieties of plutonic rocks without calling to our aid the ejections 

 of the central fire." 



§ 53. Such was the scheme put forward by the writer, in 1858 and 1859, to explain the 

 generation from a homogenous undifterentiated crust, without the intervention of plutonic 

 matters from the earth's interior, of the two great types of acidic and basic crystalline 

 rocks ; gneisses, granites and trachytes on the one hand, and doleritic rocks, green- 

 stones and basalts on the other. Regarded as an attempt to adapt the Huttoniau hypo- 

 thesis to the growing demands of the science, and to give it what it had hitherto lacked, 

 a starting point in time, and a possible exijlanation of the two types of acidic and basic 

 rocks, this scheme demands a place in the history of geology, although, in the judgment 

 of its author, it must share the fate of all other forms of the metamorphic hypothesis. 

 In recognizing the adec[uacy of a primitive unditFerentiated layer of igneous rock as the 

 sole source of the materials of the future order it, however, effected a great step towards 

 a more satisfactory hypothesis.^" 



" See, for the references to this early statement, the American Journal Science for January, 1858, (vol. xxv, p. 

 102;) also a Theory of Igneous Rocks and Volcanoes, Canadian Journal, Toronto, May, 1858 ; and Some Points in 

 Chemical Geology, in abstract in Philos. Mag. for February, and in full in the Quarterly Geological Journal for 

 November, 1859. The latter two papers are reprinted in the author's Chemical and Geological Essays, pp. 1-17. 



