COLONIAL GEOLOGY"— MELBOURNE. 



£9 



rocks, these d}-kes 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 tie 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 shown by numerous palseozoic 

 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 these, 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 Collingwood, 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 Collingwood 

 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 sanguine 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 by 

 others equally extensive, during which every moving thing came to be de- 

 stroyed, and when only thick 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 theory, 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 



