162 On a Deposit of Diatomacece at South Yarra. 



occasionally so liglit and friable^ that tlie passing breeze Avill 

 often float away the loosened diatoms from the surface of the 

 specimen under examination. Mixed with other clay^ it has 

 been used for making bricks^ but dviring the process of burn- 

 ing, the amount of contraction and distortion which super- 

 vened rendered them utterly worthless for economical pur- 

 poses, but exceedingly interesting and beautiful as opaque 

 microscopic objects. In separating the diatoms, the ordi- 

 nary routine has been followed, which is described in the 

 Quarterly Journal of Microscopic Science. Repeated wash- 

 ings in water will be necessary as a preliminary operation, and 

 then the action of acids and chlorate of potash, to clean the 

 objects from the organic matters which accompany them. 



In a foi'mer part of this paper allusion has been made to 

 the presence of undoubted marine shells, and of numbers of 

 Foraminife7'<s in certain portions of this deposit; and it is 

 also worthy of observation, that the clay in which these most 

 abound, is characterised by fewest of the Diatomacece. It 

 seems therefore an obvious and rational conclusion, that at 

 one time, probably not very remote, the waters of Port Phil- 

 lip Bay must have covered this locality. Subsequently, as the 

 land became elevated, and the communication with the sea 

 interrupted, but not altogether closed, it is not improbable 

 that here was formed a sort of lagoon, or salt-water marsh, 

 highly favourable to the growth and development of tlie 

 Diatomacece in immense myriads. That this period must have 

 been one of considerable duration, seems evident from the 

 large quantities of their silicious shields in particular parts of 

 the deposit ; and during the further elevation of the land, it 

 is possible that an interruption of fresh water into this lagoon 

 suddenly destroyed the vitality of the organisms, leaving their 

 remains in exquisite preservation, as a rich legacy to micro- 

 scopic science. 



In the careful examination of this deposit, upwards of fifty 

 different forms of diatoms may be found, in addition to 

 spicula of sponge, and the object known as Dictyocha. While 

 some of the forms are exceedingly rare, others are very abun- 

 dant ; among which is the beautiful species of Actinocyclus, 

 to which I have ventured to give the name of His Excellency, 

 the President of this Society. 



1. Actinocyclus Barklyi. Valve convex, with central 

 nodule; strise moniliform, arranged in radiating lines, and di- 

 minishing in number towards the centre; no pseudo-marginal 



