STRATlGRAPHtCAL GEOLOGY. 439 



A. Archcean and Pre-Cambrian Rocks. The great complex 

 of gneiss and crystalline schists which forms the basement of the 

 oldest fossiliferous sedimentary rocks, and had always since 

 Werner's time been divided according to lithological characters, 

 was imbued with new interest when, in 1854, William Logan 

 reported the presence of organic remains in limestone inter- 

 bedded with the ancient gneiss of Canada. The Eozoon 

 Canadense was regarded by Sir J. W. Dawson and W. B. 

 Carpenter as a foraminiferal genus, and the supposed complex 

 of Archaean schists and gneiss was accordingly placed in the 

 series of sedimentary formations. Logan (1863) differentiated 

 in Canada an older Laurentian gneiss formation and a 

 younger Huronian formation resting upon it, and chiefly 

 composed of mica schist and phyllite. Giimbel proposed a 

 similar sub-division of the basement rocks in the area of the 

 " Bavarian Forest." These divisions have not, however, been 

 verified by subsequent researches; in some parts of North 

 America it has been demonstrated that the Laurentian grani- 

 toid and gneissose masses are continuous with dykes and veins 

 in the schists and phyllites, and these intrusions must be 

 younger than the Huronian series into which they have forced 

 their way. 



The organic nature of the " Eozoon " was afterwards dis- 

 credited by King, Rowney, and Moebius (cf. p. 386), but the 

 adherents of the theory of descent argued the strong prob- 

 ability of the occurrence of organic remains in these ancient 

 pre-Cambrian rocks. And now and again other evidences of 

 organic life are found in the ancient schists and phyllites, e.g., 

 worm-burrows, sponge spicules, and traces of Algae or Proto- 

 zoa. Geologists have succeeded in areas where there has been 

 a relatively small degree of metamorphism in determining a 

 general chronological succession in the Archaean rocks. But 

 in countries of repeated crust-disturbances and great regional 

 metamorphism, the task is much more difficult and compli- 

 cated, although it has frequently been attempted. Hicks 

 (1877) distinguished in Wales and Scotland four divisions, 

 Lewisian, Dimetian, Arvonian, and Pebidian ; A. Nathorst, in 

 Sweden, differentiated three formations, a Lower Dal forma- 

 tion, a Middle Almesakra formation, and an Upper Wisingso 

 formation. 



In the year 1892, Van Hise published an exhaustive 

 account of the pre-Cambrian formation in North America, 



