J. Lomas — The Crydalline Gneisses. 539 



Sir A, Geikie, in opposing the view that the fundamental gneisses 

 and schists represent portions of the earliest crust that consolidated 

 on the surface of the globe, says:^ "The coarsely crystalline con- 

 dition, even of those portions of the gneiss which seem most nearly 

 to represent original structure, the absence of anything like scoriae 

 or fragmental bands of any kind, and the resemblances which may 

 be traced between parts of the gneiss and intrusive bosses of igneous 

 rock, compel us to seek the nearest analogies to the original gneiss 

 in the deep-seated masses of eruptive material." I may remark 

 that a coarsely crystalline condition is a measure of the rate of 

 cooling of an igneous mass rather than of its depth below the 

 surface. 



Professor Bonney says:^ "The crust itself must have solidified 

 under conditions materially diflPerent from those of a lava stream at 

 the present day ; for not only is crystallization affected by pressure, 

 but also radiation would then be comparatively slow, because the 

 atmosphere would differ much less in temperature from the solidifying 

 rock than the air now does from the surface of a lava stream. 

 . . . . The weight of the atmosphere would be augmented by 

 that of a shell of water of the area of the globe and two miles in 

 thickness ; or, in other words, the atmospheric pressure would be 

 then about 350 times its present amount." 



Another objection has been raised by Mr. T. M. Reade:^ "The 

 evidence that the Archfean rocks the world over have been buried 

 under immense bodies of sediment, of which they may have formed the 

 lower series before the deposition of the Palseozoics upon them, then, 

 seems to be irresistible." In answer to Mr. Reade I may say that 

 it would be most remarkable if every trace of these " immense bodies 

 of sediment " had been removed before the earliest sedimentary rock 

 now found was deposited. Undoubtedly there were sedimentary 

 rocks earlier than the Cambrian, such as the Torridonian and 

 Longmyndian, but wherever they are found they lie unconformably 

 on the gneisses and contain fragments of the fundamental rocks, 

 which show foliation. Foliation, then, could not be the result of 

 overlying sediments, as the structure was developed before the 

 oldest sedimentary rocks with which we are acquainted were laid 

 down. I hope to point out later, that there is evidence to show 

 that some of these gneisses have never been covered at any period 

 of the earth's history. 



According to Professor Darwin the primitive wrinkles would 

 trend about N.E.-S.W. in our latitude. The ancient gneisses of 

 Wales, Scotland, and Scandinavia, all have a strike about N.E.- 

 S.W. Comparative geology is as yet in its infancy, and information 

 regarding some of the places where Archaean rocks are exposed is 

 not easily obtained. So far as I have been able to glean information 

 on the point, I have not found an instance which is not in accord 



1 " Ancient Volcanoes," p. 116. 



^ " Story of our Planet," p. 341. 



3 n Origin of Mountain Ranges," p. 150. 



