On a Deposit of Diatonmcece at South Yarra. 161 



are exceedingly various. Some are filamentous, and in the 

 early stages of their growth very elosely resemble the Con- 

 fervae. Instead of the usual ochreous brown colour of their 

 cell-contents, a batch of Melosira, which I lately found in a 

 brackish pool near the Yarra, cxhilntcd a bright coufervoid 

 green in the younger tilaments, but gradually passing into 

 the normal brown, as the more perfect orbicular characters of 

 the frustules become developed. Other genera are connected 

 by the angles of their fi'ustules, in a kind of zig-zag chain, 

 disrupted l)y the slightest touch, from which arises the term 

 of " Brittleworts ^^ in common vernacular language, as de- 

 scriptive of the whole family. Other forms again are invested 

 Avith a gelatinous envelope, resembling that which is found to 

 exist in some genera of the Desmids; Avhile by far the greater 

 number is composed of single frustules only, becoming dupli- 

 cate in the process of self-division, which characterizes this 

 and its allied families. 



The circumstances attending the remarkable preservation 

 of these minute and delicate organizations are deserving of 

 notice. The silicious epiderm by Avhich they are invested, 

 has served to perpetuate their forms in immerous localities 

 from Avliich they have long since disappeared in a living 

 condition. In several places in the British Islands, in 

 Europe, Africa, America, and the Indies, familiar by name at 

 least to the microscopist, the long-hidden records of infu- 

 sorial organisms have been disentombed, since the silica of 

 which their frustules is composed forms one of the least 

 perishable materials Avith which Ave are acquainted. Thecitj'' 

 if Richmond, in Virginia, is said by Professor Smith to be 

 built upon a stratum of these remains, eighteen feet in thick- 

 ness ; and extensive tracts, even in the Arctic and Antarctic 

 regions, have been stated to be formed of similar deposits. It 

 is Avith some degree of satisfaction that the name of South 

 Yarra is now added to the list of these remarkable places, as 

 a rich habitat of the fossil Diatoinacete in Victoria; and Avith 

 the hope that, Avhile these varied and beautiful objects afford 

 that pleasure Avhich, in scientific pursuits, has its OAvn rcAvard, 

 they may also serve to train the eye and mind to habits of 

 correct and careful observation in our young microscopists, 

 and stinudate to still higher and nobler fields of investigation. 



The deposit, Avhen it is recently turned up, has in general 

 a very dark appearance, and the consistence of a soft tena- 

 cious clay. After a fcAv days exposure to our warm summer 

 Aveathcr^it dries into a greyish coloured substance, and becomes 



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