Observations on Mount Mary. 161' 



whole of the district, overlain in the depressions and along the 

 Werribee and tributary creeks by alluvium, and towards the 

 north by pebbly drift — to be mentioned later — and a covering of 

 varying thickness of clays of obscure origin. 



The Werribee has cut for itself a deep gorge through these 

 volcanic rocks, and though not examined the whole way from 

 Mount Mary Bridge to that at Exford, still, wherever inspected 

 at various points along the valley, no other deposits than those 

 and recent drift and alluvium were noticed. The river cliffs in 

 some places exceed 130 feet in height, and for a long way up 

 stream from the Mount Mary Bridge beds similar in appearance 

 and position to the tulF beds occur on the eastern side of the 

 river, and doubtless on the western side also. 



Now, turning to that portion of the Werribee Valley near 

 Exford, the following geological features may be seen : — In the 

 upper portion of the first gully on the western side of the river 

 below the bridge on the Melbourne-Ballarat Road, we find a thick 

 capping of drift, consisting of pebbles from the size of a man's 

 head to that of a pea, mixed with gravel, sand, and large pebbles 

 of vesicular basalt, resting on the basaltic sheet of the plains. 

 These pebbles have probably been derived from Ordovician rocks, 

 and comprise quartz, quartzites, indurated sandstones, etc. 



As the gully is followed down towards its junction with the 

 river, this pebbly drift is seen to occur on both slopes, and shows 

 in small section directly overlying the vesicular basalt. It has 

 here a thickness of something like 50 feet. 



Underlying the vesicular basalt directly is a deposit of tine, 

 sandy mudstone, of light grey and fawn colours, with a few 

 pebbles like those seen at the Werribee Bridge at Exford — to be- 

 mentioned later. This is underlain by a sharply defined bed, 3 

 feet thick as far as visible, of medium-sized pebbly gravels of 

 indurated sandstones, quartz, and quartzites. These, again, lie 

 on dense, dark, laminated, and irregularly-jointed basalt. 



The succession of rocks in descending order is thus : — 



A. — Coarse pebbly drift lying on the eroded flank and 



surface of B. 

 B. — Vesicular scoriaceous basalt of the Werribee Plains- 

 containing pieces of tachylite. 



