THE VICTORIAN NATURALIST. 25 



amorphous brown particles of a similar nature, the brown colour 

 of the sediment is apparently due. 



A possible explanation for the presence of much of the Limonite 

 may be due in this instance to the fact that in the process of 

 denudation and weathering of the tertiary basalts the iron usually 

 leaches out and forms extensive concretionary or cemented 

 gravelly deposits, locally termed " buck-shot gravels." The 

 auriferous drifts also from the north-western districts supply a 

 large proportion of limonitic or other ferruginous material. Asso- 

 ciated with the minerals described above there is also a flake of 

 amber-brown glass, with numerous gas-cavities, from the Camber- 

 well sample. 



The mineral fragments and crystals from the Victorian red-rain 

 sediment, as recorded above, have undoubtedly been derived from 

 the disintegration of the rocks ordinarily met with in the Victorian 

 area in the cotmtry to the north and west. The mineral con- 

 stituents of Dolerite and Basalt, which are so much in evidence 

 in the Melbourne dust, are not at all common in the red-rain 

 sediment, the latter material presumably originating farther to the 

 north. The accessory silicates and the other rarer and heavier 

 minerals were most likely derived from granitic and gneissic 

 rocks, and from the disintegration of lodes and veins. 



We may mention, en passant, that in his examination of the 

 sirocco dust Prof von Lasaulx noticed that the mineral con- 

 stituents consisted of the ordmary rock-forming minerals, with 

 the addition, curiously, of metallic iron particles. These latter 

 he refers to a terrestrial origin. 



Prof Silvestri, of Catania, found not only metallic iron in the 

 Sicilian sirocco dust, but also nickel and various silicates and 

 phosphates such as are found in meteorites, which led him to 

 believe that a portion of the dust was either derived from the 

 abrasion of those bodies or existed as cosmic dust, which was 

 attracted to the earth on penetrating the citmosphere. 



The terrestrial origin of the sirocco dust is now admitted on 

 nearly all sides. Prof Tacchini, who also supports this view, 

 found the specific gravity of the dust to vary from 2.3 1-2. 71, and 

 due to the invariably large proportion of silica in its composition. 



In addition to the diatoms, to be presently dealt with, there are 

 numerous pieces of vegetable tissue, more particularly fragments 

 of leaves and stems, and also numerous traces of the silicious 

 elements present in grasses, sedges, and other plants structurally 

 allied. Besides these there were numerous spore-like bodies 

 and pollen grains in samples from both localities. The 

 most striking and abundant plant remains are, however, the 

 silicious valves and frustules of the Diatomacese. Their presence 

 has been recorded in Australia on several occasions previously, 

 as we have already incidentally stated, more particularly in the 



