374 PHYSICAL STEUCTUEE AND GEOLOGY OF AUSTEALIA, 



fossils, abut on the sea in cliffs of from 300 to 600 feet in lieiglit. 

 On other parts of the coast raised beaches with recent shells are 

 common, notably round the sea boundary of the colony of Victoria. 



In the interior all these deposits are overlaid by either volcanic 

 tertiary lavas or by sands, clays, and marls which have been 

 derived from the sub-aerial weathering of the granite and other 

 rocks. The highest portions of all the edge of the table land, 

 and consequently the sources of all our rivers, are in recent 

 volcanic emanations. This is true for the whole extent of 

 Australia. These volcanic emanations are tertiary, and they are 

 all near the edge of the table land. They sweep round the eastern 

 side from north to south, curving round the south side. As far 

 as the Australian Alps they maintain a very uniform age, which 

 appears to be Miocene or later. AVest of Melbourne they change 

 their character, and become much more modern. Distinct ash 

 cones of craters are preserved, and ash beds, with remains of the 

 existing fauna and flora, are found. The extreme western limit 

 of this volcanic activity is about 100 miles south of the mouth of 

 the E/iver Murray, and here it would seem that the volcanic forces 

 in Australia died out. The raised beaches are found near these 

 craters, and have been, doubtless, elevated in connection with the 

 volcanic outbreaks. In this brief sketch no details of the nature 

 of formations have been given, and they will be now considered a 

 little more closely. 



GrEANiTE. — Two formations of Granite have been recognised 

 in Australia, and there may be more. That which forms the 

 central axis of the table land has a peculiarity which differs from 

 the outer parts of the granitic axis in this, that it is rich in 

 mineral veins. It is in such formations that the valuable deposits 

 of tin are found. They also contain veins of silver, lead, and 

 copper. Grold has also been found in granite, but this metal is 

 more common in a formation to be mentioned presently. The 

 most of the richest Australian tin deposits are stream tin, that is 

 to say, tin washed out of Granite by streams and found in their 



