The South Australian Naturalist. 63 



they are referred is known as Cambrian, and they are visited 

 by scientists from all parts of the world, because they are relics 

 of the ice age and are described as glacial tillite. The age of 

 the rocks is calculated from the time they were laid down or 

 in the process of formation ; that is, when the strata was being 

 deposited as mud to become in the course of time solid rock. 

 The remarkable fact about these rocks at Eden is that em- 

 bedded in them are quantities of various kinds of rocks that 

 are, on the face of it, extremely old. These "currants in the 

 pudding" were brought from a cold country by icebergs, and 

 as the ice was melted the rocks were deposited in the mud on 

 the sea-floor, which, many ages after, became rock and was 

 lifted up to become dry land by a subsequent earth movement. 

 This points to the fact that at one time Australia was an 

 antarctic continent. Geologists tell us that this is so, as these 

 particular evidences are proofs of glacial action. Incidentally, 

 the leader mentioned that our continent at one time was also 

 situated in the tropics, as coal, which has been found all over 

 Australia, was, and could only be, formed in a hot, moist 

 climate. Among the leader's most interestng remarks were 

 those that referred to the various kinds of rocks that were 

 seen embedded in this ancient formation. Among those men- 

 tioned were granite, which must have come from an ice-bound 

 coast; gneiss, which is granite with the mineral in layers, 

 caused by pressure ; flint or chert ; oxide of manganese, a 

 mineral from which flowers get their colour and fruits their 

 flavour ; and quartzite. On some of the outcrops the rocks 

 were covered with a green-coloured lichen, which proved a 

 very interesting object. The leader explained that this rock- 

 loving plant was the combination of two plants, the one a 

 fungus and the other an alga. The alga lives in the pores of 

 the fungus, and being green is able to carry on the work of 

 sugar and starch production by using the carbonic acid gas in 

 the atmosphere. The fungus clings to the rock by inserting 

 thread-like processes into the small holes of the rock, and 

 through these processes, which are known as mycelia, obtains 

 the necessary moisture and mineral foods. It reproduces by 

 means of spores, which are scattered from little cup-like 

 growths observable on the surface. There are a great many 

 varieties of lichens, which are variously coloured. One lichen 

 is used to make the colouring matter of litmus paper. These 

 plants act as soil-formers by disentegrating the rocks. Among 

 the trees noted were the red gum (Eucalyptus rostrata), which 

 was chiefly found growing in the creek beds. The smooth 

 white and greenish grey trunks of these gums make them a 

 beautiful sight. The box gum or peppermint (E. odorata) 



