J98 THE VICTORIAN NATURALIST. [Y'A XX lU. 



Cretaceous 



Jurassic 



Triassic. 



Permian 

 Carboniferous 

 Palseozoic Devonian 



or I Silurian 



Primary Ordovician 



Cambrian 

 I Pre-Cambrian. 



This scheme is accepted by almost all geologists, and is 

 of world-wide application. When minute, detailed work 

 is done on any set of beds, still further subdivision is 

 almost always necessary, and it is here that local names 

 are of the utmost service. 



What comes to the same thing is that, though the main 

 terms have a general application, there are usually local 

 developments in geographically distinct areas, which have 

 sufficient characteristics to warrant distinguishing terms. 



All this can be brought about properly only by a most 

 thorough and exhaustive examination of the fossils from 

 the rocks themselves. The term fossil is applied to the 

 remains of any animal or plant that has been buried in 

 the rocks of the crust of the earth by natural agencies, 

 even though it be but an imperfect and obscure im- 

 print. 



Each period of past time had its more or less charac- 

 teristic life forms, and by the remains of these, however 

 fragmentary, we know the period. Graptoli'tes, or forms 

 of invertebrate life of the hydroid type, have left abun- 

 dant fret-saw-like impressions of various shapes on the 

 rocks of many of our gold-fields, such as Bendigo, Cas- 

 tlemaine, Daylesford, &c., and belong to the Ordovician 

 part of the Palseozoic. 



Trilobites, a group of extinct crustaceans, are another 

 characteristic Palseozoic type — when perfect, somewhat 

 resembling an exalted woodlouse ; but, unfortunately, 

 these forms had the unhappy knack of parting with their 

 heads and tails, so that all sorts of fragments may usually 

 be collected — as near Kilmore, Wandong, Melbourne 

 (Moonee Valley, and along the Yarra above the Botanical 

 Gardens), Lily dale, Upper Yarra, &c. These localities 

 are of Silurian age, but it must be also borne in mind that 

 some other forms of Trilobite may denote any of the 

 other subdivisions of the Palseozoic. 



Ammonites is the old name for a group of shell-fish 

 belonging to the highest class (Cephalopoda) of the Mol- 

 lusca. In some respects the ammonite may be said to 



