540 J. Lomas — The Crystalline Gneisses. 



with the above theory.^ Some of the ridges would probably be of 

 continental importance, but with smaller corrugations riding on them. 



We will suppose now that the earth's crust has become solid, and 

 the wrinkles remain as long parallel ridges and hollows. It is 

 inconceivable that they should ever unfold again. They might 

 rise or fall as parts of greater movements, or their symmetry and 

 continuity might be destroyed by other foldings not parallel with 

 themselves, but otherwise they could only become degraded by the 

 forces of denudation. We must look upon these primitive ridges, 

 aided to a certain extent by volcanic material which has welled up 

 through the crust in later times, as the source of all the sedimentary 

 rocks. The crests have become denuded, and the products of dis- 

 integration have been transported by various agents and laid down 

 on the floors of the troughs. The material of the oldest sedimentaries 

 must have been derived from the highest parts of the ridges, and 

 that forming the newer sedimentaries must have been furnished by 

 the deeper parts of the ridges. This rule, of course, only applies so 

 long as deposition continues (in Wales practically to the end of the 

 Silurian). If the sea-bottom^ becomes raised to form land, then the 

 sedimentary rocks themselves become denuded, and the tracing of 

 a particle to its ultimate source becomes a complex problem. 



If the picture drawn above of the relief of the land in early times 

 be true, the oldest sedimentary rocks should attest the fact by their 

 characters and distribution. Professor G. M. Dawson, speaking of the 

 Archaean sedimentary rocks of Canada, says:^ "We find long bands of 

 strata, referable to the Huronian and Grenville Series, occupying 

 synclinal troughs, more or less parallel to each other and to the foliation 

 of the Fundamental Gneiss, the strata, as well as the foliation, being 

 in most cases at high angles, vertical, or even reversed." Many other 

 instances might be quoted from America, where the sedimentary 

 rocks of Pre-Cambrian age are described as being laid down in 

 long parallel troughs with sides composed of Fundamental Gneiss. 

 In Europe " the oldest beds of Bohemia form a basin some 90 m. 

 long and 10-12 m. broad, the principal axis running in a south-west 

 direction from Prague through Beraun to Pilsen. In consequence 

 of this very regular structure, the oldest beds occur at the boundary 

 and the newest in the middle of the basin, whilst the floor of the 

 trough is made up of Archeean rocks, and, above them, of un- 

 fossiliferous, phyllitic schists, called the Przibi-am schists by Lipoid, 

 which include locally conglomerate, sandstone, and oolitic limestone." ^ 



In Britain the same story is told. The Archaean rocks of 

 Anglesey and the Lleyn Peninsula, and those of the Midlands, 

 form ridges about N.E.-S.W., which bound a trough in which are 

 contained the Cambrian and Silurian deposits. Further west the 

 folds are repeated in the N.W. Highlands, and eastwards, under the 

 capping of newer rocks, into Normandy, Scandinavia, etc. 



^ Mr. R. Gascoyne, who has just returned from Chili, informs me that the strike 

 of the Archseans in that country is about N. and S. 



'^ President's Address, Section C (Geology), British Association, 1897. 

 3 Kayser-Lake, " Text Book of Comparative Geology," p. 39. 



