COLONIAL GEOLOGT— MELBOURNE. 
29 
rocks, these dykes would seem to have been thrown up in a heated state 
They occur in many places, but being generally denuded down to the level 
of the surrounding rocks, traces of their existence are only discoverable by 
Fig. 3. — View of the strata near the junction of Collins and Russell Streets. I am in- 
debted for the sketch to a paper read by M. Blandowski before the Royal Society of 
Victoria. The sketch represents the surface as looked down upon from above. 
the accidental labours of the quarryman. The fact that these (the dykes) 
are of an ancient date is most satisfactorily sho\A n by numerous pala?ozoic 
conglomerates being evidently formed from these eroded materials, and 
from their being seen to penetrate the Lower Silurian rocks, whilst the 
upper beds of the same formation rest perfectly undisturbed above. 
Another feature worthy of notice is found in the quantity of quartz 
veins with which the Silurian beds are penetrated. The black lines re- 
presenting tiiese, all having a nearly meridional strike, is quite a feature 
on maps of the districts wherein they abound. On the diggings, such 
veins are, as may be supposed, auriferous ; but quartz is found in many 
localities wherein no trace of gold can be discovered. The sandstones of 
Studley Park, east of CoUingwood, are often singularly intersected by this 
mineral, some of which, even in this locality, would seem to contain specks 
of the precious metal, since gravel brought from the neighbourhood often 
displays gold in minute portions. I may mention that the CoUingwood 
Mining Company are sinking a shaft through the " blue stone " (basalt) 
for the purpose of testing the bottom covered by the detritus of these 
rocks, and are sangmne of success. 
The fossils in the Melbourne Silurian formation are tolerably nume- 
rous ; but although many of the beds contain a profusion of marine exuvia, 
literally cemented together, like pebbles in a conglomerate, others are 
apparently barren of all vestiges of life or its evidences. Such a state of 
things would seem to tell of periods of repose and subsequent convul- 
sions, long ago, when life became marvellously abundant, followed b}' 
others equally extensive, during which every moving thing came to b3 de- 
stroyed, and when only tliick beds of sand, fine clay, and dense impalpa- 
ble mud accumulated in sea-bottoms untenanted by a single organism en- 
dowed with life, unenlivened by even a vegetable form. 
As avoiding such a theorv, I am reminded of an hypothesis put forth 
by the late Hugh Miller, that in somewhat similar barren rocks alterna- 
ting with a profusion of organisms, the shells had probably sunk by gra- 
vity through the quicksand surrounding them, and that the fossiliferous 
beds so formed had subsequently been cleared of the remaining sandy 
particles by the gradual percolation of water through their midst. The 
