492 TRANSACTIONS OF SECTION C. 
of carbonate of lime, which is so characteristic a feature of most Cambrian and 
pre-Cambrian sediments, indicates that the bulk of the contemporary organisms 
had chitinous shells or were soft-bodied. Palaeontology begins with the appearance 
of hard-bodied organisms ; it can only reveal to us the dawn of skeletons, not the 
dawn of life. We are dependent for knowledge of the climate and geography of 
Eozoic time to the evidence of the sediments, of which there are great thicknesses 
beneath the fossiliferous rocks in most parts of the world.! 
II. The Geology of the Inner Earth. 
Now that this geological survey of the earth is in rapid progress; while the 
history of life has been written at least in outline; the chief fossils, minerals, and 
rocks have been described and generously endowed with names; and the manifold 
activity of water and air in moulding the surface is duly appreciated, it is not 
surprising to find that the centre of geological interest is shifting to the deeper 
regions of the earth’s crust and to the problems of applied Geology. The secrets 
of these deeper regions are both of scientific and economic interest. They are of 
scientific importance, for it is now generally recognised that the main plan of the 
earth’s geography and the essential characters of the successive geological systems 
are the result of internal movements. The relative importance of those restless 
external agents that we can watch, denuding here and depositing there, has been 
exaggerated ; probably they do little more than soften the outlines due to the 
silent heavings produced by the colossal energies of the inner earth. 
The study of the deeper layers of the crust is of economic interest, for, with 
keener competition between increasing populations and with the exhaustion of 
the most easily used resources of field and mine, there is growing need for the 
better utilisation of soils and waters, and for the pursuit of deeper deposits 
of ore. 
If a shaft be sunk at any point on the earth’s surface, a formation of Archean 
schists and gneisses would probably always be reached ; and, working backward, 
geological methods always fail at last—in primeeval, Archeean darkness, The 
Archean rocks still hide from us the earlier period of the earth’s history, including 
that of all rocks which now lie beneath them. But already there are indications 
that the mystery of the ‘ beyond’ is not so impenetrable as it seemed. 
1. The Nebular and Meteoritie Hypotheses.—The eighteenth century explained 
the history of the earth by the nebular hypothesis of Laplace. Geologists respect- 
fully adopted this idea from the astronomers; they accepted it as one of those 
essential facts of the universe with which geological philosophy must harmonise. 
The resulting theory represented the earth as originally a glowing cloud of incan- 
descent gas, which slowly cooled, until an irregular crust of rock formed around a 
gaseous or molten core; as the surface grew cooler, the depressions in the crust 
were filled with water from the condensing vapour, forming oceans which became 
habitable as the temperature further fell. The whole earth was thought to have 
had a long period with a universal tropical climate, under which coral reefs grew 
where flow our polar seas, and palms flourished on what are now the Arctic 
shores. Still further cooling had established our climatic zones; and it was pre- 
dicted that in time the polar cold would creep outward, driving all living beings 
toward the equator, until at length the whole earth, like the moon, would become 
lifeless through cold, as it had once been uninhabitable through heat. This 
theory has permanently impressed itself on geological terminology; and its 
corollaries, secular refrigeration and the contortion of the shrinking crust, once 
dominated discussions concerning climatic history and the formation of mountain 
chains. This nebular hypothesis, however, we are now told, is mathematically 
1 Such are the Algonkian sediments represented by the Huronian and Algonkians 
of America, the Algonkians of Scandinavia, the Karelian of Finland, the Briovarian 
of North-West France, the Heathcotian of Australia, the Transvaal and Swaziland 
systems of South Africa, the Dharwar and Bijawar systems of India, the Itacolumnite 
series of Brazil, &c. 
