172 On the Sections of the Delta of the Yarra, 



rapidity. The actual surface consists of a series of long rolls, 

 whose axes run approximately parallel to the present shore 

 line. In some cases a single roll can be traced continuously 

 for two or three miles. The axes are also at right angles to 

 the prevailing windi5, running E. and W. In the established 

 land the ridges are sandy, and grow bracken only, while the 

 hollows in which water has been able to lie yield a good 

 soil, often even a solid turf. 



The silt holds water. In consequence a difficulty was 

 encountered in making the canal, for the surface-waters, 

 accumulating on the top of the silt, emerged as springs or 

 oozed from the sides of the cutting. The vegetation, chiefly 

 bracken, of the surface has formed a certain amount of 

 bumus. The atmospheric waters passing through have 

 become sufficiently impregnated with acids to dissolve the 

 iron of the (probably basaltic) sands, and appeared as reddish- 

 brown streamlets, disfiguring and injuring the slopes of the 

 work. Wherever the course of such a runnel is arrested — 

 as where it flows over a tiny fall into a miniature pool — a 

 foam is thrown up, which, from its soapy touch and ochreous 

 colour, reminds one of meerschaum. I made, with the aid 

 of my pupils, a rough analysis of the solid constituent of the 

 foam vesicles, and found that it was a compound silicate of 

 aluminium, with a good proportion of ferrous oxide and 

 traces of ferric oxide, but with no magnesia. The water per- 

 colating through the sand takes up other matters in solution, 

 and, upon evaporation at the free surface exposed to the 

 atmosphere, leaves the solids as incrustations. Such white 

 and yellow patches were here and there conspicuous, both 

 on sand and silt below. The white incrustations consisted 

 of sodium and magnesium chlorides, and the yellow of 

 ferric chloride. 



The silt forms the greater part of the West Melbourne 

 Swamp, and betrays there also its estuarial origin. Mr. 

 Davies has shown me the skull of a dolphin found 10 feet 

 below the surface at one point, and others have been ob- 

 tained. Mr. Bale, F.R.M.S., has furnished me with a list of 

 diatoms found in the deposits of the West Melbourne Swamp, 

 which are notable for their richness in those organisms. The 

 list is not exhaustive, but includes all the commoner forms, 

 and these, without exception, are proper to brackish or salt 

 water. The species comprised Campylodiscus Dcemelianus, 

 C. echeneis (= C. crihrosus, C. argus), G. clypeus, Synedra 

 gracilis (— S. pulchella var.), Nitzschia tryhlionella (= T. 



