14 DE. THOMAS STEREY HUNT ON THE 



originally from the fused material of the globe, so that the proof of such au origin by 

 re-fusion is not established beyond a doubt." 



§ 28. It is not clear whether, according to Dana, we have anywhere this hypothetical 

 primitive or truly Archœan rock exposed, since, speaking of the Laurentian series, which 

 he also calls Archœan, he says at the same time : — " These Laurentian rocks are made out of 

 the ruins of older Laurentian, or of still older Archœan rocks ; that is to say the sands, 

 clays and stones made and distributed by the ocean, as it washed over the earliest-formed 

 crust of the globe. The loose material, transported by the currents and the waves, was 

 piled into layers, as in the following ages, and vast accumulations were formed ; for no 

 one estimates the thickness of the recognized Laurentian beds as below thirty thousand 

 feet." Lest he should be supposed to hold to his former theory of the volcanic origin 

 of these supposed detrital matters, which formed the Laurentian, he now declares " They 

 have no resemblance to lavas or igneous ejections." "' 



These crystalline stratified rocks are thus not that universal Archœan terrane which 

 was the first-formed crust of the cooling globe. The imagination is at a loss, however, to 

 understand the nature of the disintegrating process, or the source of the materials which 

 in the Laurentian period were, according to this hypothesis, spread over vast areas to a 

 depth of not less than thirty thousand feet, and seeks in vain for the site of the vanished 

 Atlantis which furnished this enormous amount of mechanically disintegrated rock. 



§ 29. Clarence King, in 18*78, gave us a clear and admirable discussion of the same 

 detrital metamorphic theory, and argued, as Dana had done before him, that the depression 

 of sedimentary strata below the surface of the earth, even to great depths, is not sufficient 

 to effect their crystallization ; since basal paleozoic beds which have been buried beneath 

 30,000 feet or more of sediments are now seen, when exposed by great movements of 

 elevation, and by erosion, to present no evidences of crystallization or so-called alteration. 

 King, however, did not reject volcanic action as a source of detritus, for in discussing 

 the origin of the great beds of serpentine and of olivine-rock which are often met with in 

 the older crystalline schists, he says, " olivine-bearing rocks are among the oldest eruptive 

 bodies," and then asks, " may not olivine-sands, like those now seen on the shores of the 

 Hawaiian Islands, have been then, as now, accumulated by the mechanical separation of 

 sea-currents, and subsequently buried by feldspathic and quartz-sands." He thus looks 

 to volcanic eruptions for the source of olivine and serpentine beds, and adds, " I see no 

 reason to ask for a different origin for the magnesian silicates than for the aluminous 

 minerals," ^ the eruptive source of which is thus implied. A similar hypothesis of the 

 formation of beds of olivine-rock and serpentine from accumulations of volcanic olivine- 

 sand, has since been maintained by Julien, whose paper is mentioned further on, § 37. 



§ 80. Other geologists, besides King, have in later times advocated a similar volcanic 

 hypothesis of the origin of crystalline rocks. A. Kopp, iji 18*72, taught that granite 

 is an altered trachytic lava, and that gneiss may be derived from the detritus of trachyte 

 or of granite, while dol critic lavas in like manner give rise to the various greenstones. 

 The transformation of these is supposed to be effected through the intervention of 



"' Dana, Manual of Geology, 3rd ed. 1879, pp. 147, 154, 155, also 720. 

 " Geology of the Fortieth Parallel, vol. I, p. 117. 



