406 TRANSACTIONS OF SECTION C. 



sedimentary type peculiar to the early stages in the formation of a habitable 

 crust. If such a type existed, it has been lost to us through subsequent 

 metamorphism, amounting to the actual fusion and redistribution of its con- 

 stituents. The Grenville series of North America, first recognised by Logan, 

 has been studied in considerable detail.' Its relation to the Keewatm senesof 

 Canada is unknown, but it rests on a floor of granitoid rock, which is intrusive 

 in it, and which belongs to the oldest of various irruptive groups. The Grenville 

 series includes conglomerates, false-bedded quartzites, and a development of 

 limestone that is altogether exceptional for pre-Cambrian times. In Finland," 

 sediments have been traced down to the layer where their original characters 

 vanish in a general ' migmatitic ' ground. The Bottnian and the still older 

 Ladogan systems alike provide us with strata in which primary characters have 

 been preserved. Conglomerates and phyllites occur among them, and near 

 Tampere (Tammerfors) the seasonal stratification is as well recorded in a 

 Bottnian shale as it is in the Pleistocene clays made famous in Sweden by 

 De Geer. Vein-gneiss (Adergneis) underlies these ancient systems, and represents 

 their destruction by the injection of granite from below. It is to be noted 

 that J. J.' Sederholm '° believes that in several places in Finland the ' basement 

 complexes of the typical Archaean sedimentary formations ' have been preserved. 

 These, however, may well be also sedimentary, and thus similar in origin to the 

 later complexes above them. Their surfaces must be due to denudation, and 

 their igneous constituents were intruded into rocks which may have been 

 merely a cover worn from still older masses. 



If we accept the meteoritic and planetesimal hypotheses of Lockyer and 

 Chamberlin, it is quite possible to argue that tlie primitive crust was never 

 molten as a whole. It may never have lost its fragmental structure, which was 

 original and due to accretion from without. When agents of denudation came 

 to work upon it, a chemical as well as a mechanical sifting of various materials 

 came about. The oldest sediments were less differentiated than their suc- 

 cessors; chemical adjustments may then have been made in response to demands 

 from the interior of the globe"; and ultimately normal types of sediment — 

 that is, types to which we are now accustomed — began to gather in hollows of 

 the surface. So far, Hutton's position becomes strengthened by the postu- 

 lation of an unfused planetesimal crust, and the restriction of molten masses 

 and hydrothermal activity to the interior of a consolidating globe. 



The doctrines of Laplace, however, led Hutton's immediate successors to see 

 in crystalline schists the products of abnormal sedimentation. In their view, a 

 molten globe became surrounded by a slowly consolidating crust, and highly 

 heated waters, playing upon this, deposited crystalline material on the floors of 

 primordial seas.'^ Among other workers on pre-Cambrian rocks, T. G. Bonney '^ 

 has upheld the view that the conditions under which schists were formed have 

 not been repeated in later geological times. This is, of course, true if they are 

 deposits from hot solutions and were laid down at the surface of the earth. 



R. A. Daly " has reasoned that we may accept the planetesimal view and yet 

 believe that a molten surface prevailed at some time over the whole globe ; and 

 A. Holmes, 1^ in a recent and lucid paper, supports these arguments from the 



* F. D. Adams and A. E. Barlow, ' Geology of Haliburton and Bancroft 

 Areas,' Geol. Surv. Cmmda, Mem. 6 (1910), p. 36. 



° J. J. Sederholm, ' Ueber eine archaische Sedimentformation im siidwest- 

 lichen-Finland,' Bull. Comm. cjcol. Finlande, No. 6 (1899), p. 215. 



'" Oi}. cit. No. 6, p. 213, and ' Om Granit och Gneis,' ibid., No. 23 (1907), 

 p. 100. 



" See C. H. L. Schwarz, Causal Geology (1910), p. 11. 



" G. P. Scrope, Considerations on Volcanos (1825), p. 226. 



" Presidential Address, Quart. Journ. Geol. Soc. London, vol. xlii. (1886), 

 Proceedings, p. 110. See also T. Sterry Hunt, ' Etudes sur les Schistes 

 cristallins,' C.B., Congres geol. internal. 1888, p. 65. 



" Igneous Hocks and their Origin (1914), p. 159. 



" ' Radio-activity and the Earth's Thermal History,' Geol. Mag. 1915, p. 105. 

 On the power of radio-active substances to promote rock-fusion see, however, 

 J. P. Iddings, The Problem of Volcanism (1914), p. 141. 



