C— GEOLOGY 6 1 



although this is a side-issue of purely scientific investigations, we find at 

 every turn that the door has been opened to important industrial appli- 

 cations of the facts so gathered, and geology in consequence continues to 

 play its role as one of the most valuable instruments in the service of Man. 

 Germane in this connection are the recent and active developments in 

 our knowledge of the formation and emplacement of the deposits of useful 

 metals and non-metals. These advances have resulted from the realisation 

 that the problems involve the application of physical and chemical laws, 

 and that ores, veinstones, and salts ultimately have a genetic connection 

 with sub-crustal magmas. In those cases where superficial deposits 

 conceal from the geologist possible mineral wealth existing at depth, he 

 is now able to call to his aid the methods of applied geophysics — gravi- 

 tational, magnetic, electric, radio-active, and seismic. 



The advances in the technique of geophysical prospecting in recent 

 years are so outstanding as to justify our pausing for a moment to refer 

 to them. Not only is precision given to estimates of the extent and 

 depth of ore-bodies of large dimensions, and of irregular alluvial ore 

 deposits covered by overburden, but the location of the water-table 

 underground, as well as the distinction between fresh and saline waters, 

 and the demarcation of salt-deposits and of the cavities occupied by brine, 

 can also be effected. Estimation of the depth of buried topographic 

 features, and the determination of thickness of overlying deposits such 

 as Glacial Drift (of great importance in establishing foundations), or of 

 detritus like that formed by tropical weathering, can now be made with 

 considerable success. The position of old mine-workings, bad ground, 

 and flooded areas can be determined with safety and at less expense 

 than by the older method of exploration, which might at any moment 

 result in loss of life. It should be emphasised, however, that geophysical 

 prospecting supplements and gives precision to the ordinary geological 

 methods of investigation — it cannot replace them. 



As distinct from their formation, the concentration of sparsely dis- 

 seminated elements and compounds into workable masses is due to 

 chemical and physical processes ; similarly, the action of plants and 

 animals results in the concentration of energy in such fuel-products as 

 the various coals, oil-shales and petroleum. Exactly in what manner 

 deposits of the latter type formed and accumulated in commercial quanti- 

 ties is by no means clear, nor for that matter is it always evident in the 

 case of metallic ores (as was manifest from the discussions in this Section 

 at the Centenary Meeting). But we may hope for further enlighten- 

 ment from experimental and synthetic work at present in progress, 

 especially when it guides and is guided by further field- investigations. 



Time was when the establishment of the truth of organic evolution 

 and the concomitant inquiry into the manner in which the minute changes 

 in organisms arose was all-sufficient for the majority of thinkers. But 

 Eduard Suess, with a wider and deeper grasp of the essentials of earth- 

 history, approached more nearly to a philosophic conception, when he 

 wrote in an oft-quoted passage of ' those great physical changes in com- 

 parison with which the changes in the organic world only appear as 

 phenomena of the second order, as simple consequences.' To determine 



