150 THE BUILDING OF EASTERN AUSTRALIA 



The Reconstruction of Pal^ogeography. 



Just as the historian and the antiquarian in their 

 discussions on events prior to the exact historical period 

 speak of the stone age, the bronze age, and so forth, 

 dividing early historical time according to the nature 

 of the debris characterising the age, so the geologist, 

 who has no exact conception of the duration of his periods, 

 divides geological time into the age of fishes, the age of 

 reptiles, the age of Brachiopods, and so forth. 



Just as the historian divides time into periods and 

 his periods into dynasties, so the geologist divides his 

 geological time into periods, and his periods into epochs. 

 In the same way as the historian speaks of the Heroic 

 Age or Era, so the geologist speaks of the Palaeozoic 

 Age or Era. The historian has his shepherd king period. 

 Plantagenet period, and so on ; the geologist, likewise, 

 has his Devonian Period, Miocene period, and so on. 

 Just as the historian speaks of the dynasty of the 

 Ptolemys, Hanover dynasty, &c., so the geologist has 

 geological horizons based on the predominance of some 

 particular dynasty of animal or plant life. 



Our knowledge of the geograph}^ of past geological 

 ages is gathered from the study of the fossilised remains 

 of plants and animals. Of all petrifactions, none are 

 so important to the geologist as shallow water marine 

 organisms ; because of their abundance in the fossil 

 state, and their uninterrupted sway during the long ages 

 they afford us landmarks, not only for the division of 

 geological time into periods, but also into horizons and 

 stages. The long persistency of each genus allowed 

 it to differentiate into sub-genera and species, which, 

 besides being very absorbing studies for the evolutionist, 

 are also of great value in delimiting the minor divisions 

 of geological time. 



In the following pages it is taken as an axiom that 

 a great accumulation in any place of marine fossils 

 indicates close proximity to the shore line at the time 

 of deposition. This follows from two considerations. 

 In the first place the waters of the continental shelf 

 are better adapted, both as regards temperature and 

 food supplies, for plant and animal life. In the second 

 place, the opportunities for organisms to be preserved 



