■2Q4. THE nCTORIAN NATURALIST. [Tol. XXIII. 



The oldest rocks close to Port Phillip are ordovician in 

 age. There are slates and sandstones at jSIount Eliza and at 

 Red Hill, near Dromana, with fossils in them like those 

 of Bendigo. The granite of Mount Martha and other 

 places near is younger than these rocks, for veins of 

 granite penetrate the slates. Younger, again, than these 

 rocks are the coal-bearing sandstones and shales of the 

 Otways and South Gippsland. They are called Jurassic, 

 for they are, so the fossils tell us, the same age as the 

 rocks of the Jura Mountains. Nearer to us than the 

 Otways we find them in the Barrabool Hills, at Port- 

 arlington, and on the beach at Mount Eliza. They con- 

 tain the remains of only land and fresh-water animals 

 and plants — giant carnivorous reptiles, fish, and many 

 kinds of ferns. So they must have been deposited in a 

 lake. They are lake-sandstones. 



After these rocks were formed, another series of lake 

 or swamp deposits was laid down. These are the leaf 

 beds, or lignite beds, and in our excursion we shall ex- 

 amine them closely. Then came an outpouring of blue- 

 stone, known for convenience as the older volcanic rock. 

 This we shall also see on the beach. Then the land 

 sank, and the clays, limestones, and sands of eocene age 

 were deposited. In these beds vou have already been 

 digging for fossils. Then came the newer bluestones, or 

 lavas, of our Avestern plains, as shown from Williams- 

 town to near Geelong. The voungest rocks of all are the 

 sand dunes and alluvial deposits. 



Port Phillip is a drowned valley with a very flat floor. 

 On this floor we can still trace the course of the Yarra, 

 and still more clearly that of the Werribee. As it sank, 

 its eastern boundary was marked by a great fault, or 

 fracture, which can be traced from Frankston to the 

 Schanck. Another bounding fault runs from Geelong to 

 Portarlington, and much further east and west. 



At first the harbor was widely open, from Ocean Grove 

 •lo the Schanck. Then sand dunes barred it. The lecturer 

 devoted a good deal of time to discussing the tvpes of 

 flora found on the various rocks. The real governing 

 factor of plant distribution is water. The amount de- 

 pends, of course, chiefly on the rainfall, but is modified 

 by the annual distribution of that rainfall, and to a 

 marked extent by the water capacity of the rocks. Solid 

 bluestone holds practically none. So plant growth on 

 solid bluestone in our climate lakes place only in wet 

 weather. Nothing can live in the driest weeks of summer. 



