158 
Geology of Sydney. 
natural orders are quite distinctive. The Myrtacece are 
remarkable for their oil glands, the leaves of Rutacece 
are known by their oil dots, the Proteacece by the fibres 
of the leaves, and the leaves of Conifers and Cycads are 
also characteristic. But palaeontologists, such as Heer 
and Ettingshausen, go further, and distinguish fossil 
leaf from leaf, in a manner quite incomprehensible to 
the student. A shepherd can see a different face on 
every sheep in his flock, while to an ordinary observer 
there would be no possibility of distinguishing them. 
So it is when botanists give themselves up to the 
study of fossil plants : they doubtless become skilled 
to an extent quite beyond the reach of a beginner. 
The fossil plants found immediately around 
Sydney differ entirely from anything now living in 
Australia. At the same time, they are not so far 
removed from living forms as, for example, the plants 
of the Carboniferous period. The whole history of the 
earth, as far as plants are concerned, may be divided 
into three great eras : the first and most ancient, 
characterized by giant lycopods, horsetails and ferns ; 
the second, characterized by ferns, lycopods, cycads, 
conifers, and palms; and the third, and more recent, 
characterized by such plants as we see clothing the 
earth to-day — dicotyledons for the most part. The 
Hawkesbury Sandstone, of Triassic age, belongs, of 
course, to the second of these eras. 
Let us picture to ourselves one of these Triassic 
forests that once clothed the hills and gullies where 
Sydney and its harbour stand to-day. But, first of 
