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THE CLIMATES OF THE GEOLOGICAL PAST. 



By H. J. JENSEN, D.Sc. 



Bead before the Boyal Society of Queensland, 26th September^ 



1909. 



The important discovery of the Shackelton Antarctic 

 Expedition of coal seams, within a few degrees of the 

 South Pole, at an elevation of 10,000 feet, is another piece 

 of evidence that this elevated and frozen region was once 

 situated near sea level, and was enjoying a warm or tem- 

 perate cHmate. 



The cause of an " Ice Age," and the cau«o of a warm 

 cycle such as may produce a luxuriant tropical vege- 

 tation in Arctic regions, are subjects Avhich have given 

 rise to more controversy than perhaj)s any other scientific 

 question, excepting the modern problems, of radio-activity. 



Although no single theory has been found adequate 

 to account for an ice-age, still we get closer to the solution 

 of the problem as the years roll on. The American School 

 of Geologists, by their lucid reasoning, have done much 

 to help clear up the question. 



The ice-ages of greatest geological significance, that 

 is, producing the most widespread effects, were the 

 Cambrian Ice Age in the dawn of life on earth, the Permo- 

 Carboniferous ice age in the period when coal measure^ 

 were laid down, and tht late Tertiary when Europe was 

 covered with extensive glaciers, and an ice age prevailed 

 on Mount Kosciusko and Tasmania. 



The early Cambrian Era was a period of great con. 

 tinental extension and uplift. Either the continents rose 

 and grew larger at the expense of the sea — or M'hat really 

 amounts to the same thing — the oceans grew deeper so that 

 the waters sank or became confined to smaller areas. One 

 of the results of this continental extension was that arms 

 of the pre-Cambrian seas became isolated, and were turned 

 into lakes situated at compaiatively high altitudes. 



E — Royal Society. 



